Gaschem

The five SuperFast rate-law helper functions migrated from GasChem.jl@8c12c048482b515fb8eb2110bf8ab4b4f4e71309 src/SuperFast.jl — the reusable builder functions the SuperFast() chemical mechanism uses to construct the rate coefficient of every gas-phase reaction. Each is migrated as its own observed-only algebraic `models` entry: rate_toppb (SuperFast.jl:6) the constant-rate / `constant_k` converter, arrh (:33) the modified-Arrhenius workhorse, arr_3rd (:64) the third-body / Troe-falloff law, rate_2HO2 (:102) the HO2+HO2 law with water-vapour enhancement, and rate_OH_CO (:142) the JPL 15-10 OH+CO law. Upstream each function returns a one-variable ReactionSystem (`@variables k(t)`); the composed builders (arr_3rd, rate_2HO2, rate_OH_CO) compose `arrh` sub-systems. This file reproduces each function's compiled rate as a topologically-ordered cascade of `type: state` algebraic equations whose named intermediates mirror the upstream Julia locals and sub-system k's verbatim, with the Arrhenius coefficients exposed as `type: parameter` (defaults taken from the representative SuperFast reaction each builder serves). All five models are purely algebraic — no time derivatives — so each rate coefficient is constant in time. Units follow the upstream's mixed CGS / ppb system (rate coefficients in 1/(s*ppb), Arrhenius pre-exponentials in cm^3/molec/s).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

The five SuperFast rate-law helper functions migrated from GasChem.jl@8c12c048482b515fb8eb2110bf8ab4b4f4e71309 src/SuperFast.jl — the reusable builder functions the SuperFast() chemical mechanism uses to construct the rate coefficient of every gas-phase reaction. Each is migrated as its own observed-only algebraic `models` entry: rate_toppb (SuperFast.jl:6) the constant-rate / `constant_k` converter, arrh (:33) the modified-Arrhenius workhorse, arr_3rd (:64) the third-body / Troe-falloff law, rate_2HO2 (:102) the HO2+HO2 law with water-vapour enhancement, and rate_OH_CO (:142) the JPL 15-10 OH+CO law. Upstream each function returns a one-variable ReactionSystem (`@variables k(t)`); the composed builders (arr_3rd, rate_2HO2, rate_OH_CO) compose `arrh` sub-systems. This file reproduces each function's compiled rate as a topologically-ordered cascade of `type: state` algebraic equations whose named intermediates mirror the upstream Julia locals and sub-system k's verbatim, with the Arrhenius coefficients exposed as `type: parameter` (defaults taken from the representative SuperFast reaction each builder serves). All five models are purely algebraic — no time derivatives — so each rate coefficient is constant in time. Units follow the upstream's mixed CGS / ppb system (rate coefficients in 1/(s*ppb), Arrhenius pre-exponentials in cm^3/molec/s).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

Fundamental mass-conservation (budget) equation for an atmospheric species in a single reservoir, from Seinfeld & Pandis (2006) Ch. 2 (Atmospheric Trace Constituents), Eqs. 2.1-2.2, pp. 25-30. The reservoir mass Q evolves under the balance of transport (inflow minus outflow) and chemistry (production minus removal): dQ/dt = (F_in - F_out) + (P - R_removal) — the most basic statement of a trace-species budget, on which the lifetime, multiple-removal and tropospheric-budget formulations of the same chapter are built. The component additionally computes two diagnostic decomposition terms: the net transport contribution net_transport = F_in - F_out and the net chemistry contribution net_chemistry = P - R_removal; their sum is dQ/dt, and the steady-state condition (Eq. 2.2) dQ/dt = 0 ⇔ F_in + P = F_out + R_removal is reached when net_transport = -net_chemistry. One time-resolved ODE state (the reservoir mass Q) plus two observed (algebraic) diagnostic states (net_transport, net_chemistry); the four flux terms F_in, F_out, P, R_removal are externally-supplied inputs encoded as parameters. Migrated from GasChem.jl@8c12c048 src/AtmosphericLifetime.jl:64 (`AtmosphericBudget` @component); the upstream removal-rate @variable `R` is renamed `R_removal` here because the ESS schema reserves the bare name `R` for the ideal gas constant.

Planck's blackbody radiation law (Seinfeld & Pandis 2006 Ch. 4, Eq. 4.2) — the monochromatic emissive power F_B_λ of a blackbody at temperature T as a function of wavelength λ via Planck's constant h, the speed of light c, and the Boltzmann constant k_B: F_B_λ = 2π·c²·h·λ⁻⁵ / (exp(c·h/(k_B·λ·T)) - 1). The component is observed-only: one algebraic equation on one state variable (F_B_λ the monochromatic emissive power per unit wavelength in W/m³) driven by two input parameters (T temperature in K, λ wavelength in m) and four constants (h Planck's constant, c speed of light, k_B Boltzmann constant, π_val mathematical π as a Float64 value). No time derivatives, no PDE, no coupling. Migrated from GasChem.jl@8c12c048 src/radiation_fundamentals.jl:73 (`BlackbodyRadiation` @component). The Planck function is the spectral energy density of thermal radiation from an opaque, non-reflective body in thermodynamic equilibrium — the foundational equation of quantum radiative transfer. Integrating F_B_λ over all wavelengths gives the Stefan-Boltzmann total flux σT⁴ (see stefan_boltzmann.esm); the wavelength where F_B_λ peaks is λ_max = b/T from Wien's displacement law (see wien.esm). At the default T=5800 K (Sun's effective surface temperature) and λ=500 nm (visible green, the canonical solar-peak wavelength), F_B_λ ≈ 8.46e13 W/m³ — the peak intensity that anchors the Sun's irradiance at Earth's distance and the solar-driven photochemistry of the atmosphere. At T=300 K (Earth surface) and λ=10 μm (thermal-IR), F_B_λ ≈ 3.12e7 W/m³ — the canonical longwave outgoing radiation peak that drives the planetary energy balance.

Stratospheric bromine catalytic ozone-destruction cycle (BrOx). Three ODEs (Br, BrO, HOBr) and two algebraic family identities (BrOx = Br + BrO; Bry = Br + BrO + HOBr). Reactions: Br + O3 → BrO + O2 (Arrhenius); BrO + O → Br + O2; BrO + ClO → Br + Cl + O2 (constant rate); BrO + HO2 → HOBr + O2; HOBr + hν → OH + Br (photolysis). Unlike chlorine, bromine has no stable HBr reservoir because Br + CH4 is endothermic (Seinfeld & Pandis Page 169). Bromine is approximately 50× more effective than chlorine in destroying ozone on an atom-for-atom basis. Migrated from GasChem.jl@8c12c048 src/StratosphericChemistry.jl:390 (`BrOxCycle` @component). Rate coefficients converted CGS → SI: cm³/molec/s × 1e-6 → m³/s.

Stratospheric Chapman mechanism for ozone production and destruction (Seinfeld & Pandis 2006 Ch. 5, §5.2, Eqs. 5.1-5.17). Two-state ODE on atomic oxygen O and ozone O3 driven by the four canonical Chapman reactions: O2 photolysis (j_O2), three-body recombination O + O2 + M → O3 + M (k2 with power-law T-dependence (T_ref/T)^2.4), O3 photolysis (j_O3), and the O + O3 → 2 O2 odd-oxygen sink (k4 with Arrhenius temperature dependence). Odd oxygen Ox = O + O3 is *not* exactly conserved — the Chapman cycle has a net Ox source (2·j_O2·O2·M from O2 photolysis) balanced against an Ox sink (2·k4·O·O3 from the O+O3 reaction) — but on short timescales (≲ 10 s under default mid-stratosphere conditions) the net change is small (~4e-5 relative drift) and the upstream test treats it as quasi-conserved at rtol=1e-4. Migrated from GasChem.jl@8c12c048 src/StratosphericChemistry.jl:51 (`ChapmanMechanism` @component). Rate coefficients carry SI units throughout, converted from Seinfeld & Pandis CGS values via cm^6/molec^2/s × 1e-12 → m^6/s for the 3-body k2 and cm^3/molec/s × 1e-6 → m^3/s for the bimolecular k4.

Climate-feedback diagnostic (Seinfeld & Pandis 2006 Ch. 23 §23.4 Eqs. 23.1-23.4 and Eq. 23.7 p. 1045) — the linear-response relation between a top-of-atmosphere radiative forcing perturbation ΔF and the equilibrium surface temperature change ΔT_s through the feedback-amplified climate sensitivity λ. Six observed-only algebraic equations on six state variables (ΔT_s the feedback-amplified equilibrium response, ΔT_0 the no-feedback Planck response, λ_0 the no-feedback sensitivity factor, ΔF_e the efficacy-weighted effective forcing, ΔF_r the forcing equivalent of realized warming, ΔT_unrealized the warming commitment) driven by five input parameters (ΔF the forcing perturbation, λ the feedback-amplified sensitivity, λ_CO2 the CO₂-doubling sensitivity reference, E_i the efficacy of the forcing agent, ΔT_r the realized warming to date) and two reference constants (ΔF_2xCO2 the CO₂-doubling radiative forcing, ΔT0_2xCO2 the no-feedback temperature change for CO₂ doubling). No time derivatives, no PDE, no coupling. Migrated from GasChem.jl@8c12c048 src/climate_forcing.jl:32 (`ClimateFeedback` @component). The component extends the no-feedback Planck response of the sibling `ClimateSensitivity` model (components/gaschem/radiation/climate_sensitivity.esm, S&P §4.2 Eqs. 4.8-4.10) by introducing the feedback-amplified sensitivity factor λ and the warming-commitment relation ΔT_unrealized = (ΔF - ΔF_r)·λ that captures the lag between achieved (ΔT_r) and equilibrium (ΔT_s) warming under a non-zero forcing perturbation. At Earth's nominal 2×CO₂ forcing ΔF = 3.7 W/m² and λ = 0.8 K·m²/W (IPCC AR4 central estimate), the component reproduces the textbook canonical ΔT_s ≈ 2.96 K equilibrium warming (S&P Page 1040), λ_0 ≈ 0.338 K·m²/W no-feedback Planck response, and ΔT_unrealized ≈ 0.49 K warming commitment for the present-day p. 1045 scenario (λ = 0.7, ΔF = 1.7, ΔT_r = 0.7).

Climate-sensitivity diagnostic (Seinfeld & Pandis 2006 Ch. 4, Eqs. 4.8-4.10) — the linear-response relation between a top-of-atmosphere radiative-forcing perturbation ΔF_net and the resulting change in planetary equilibrium temperature ΔT_e through the no-feedback climate-sensitivity factor λ_0 = 1 / (4·σ·T_e^3) = T_e / (4·F_L). The component is observed-only: four algebraic equations on four state variables (ΔF_net the net forcing, λ_0 the sensitivity factor, ΔT_e the temperature response, F_L the reference longwave flux) driven by three input parameters (T_e the reference equilibrium temperature, ΔF_S the forcing-side perturbation, ΔF_L the longwave-side perturbation) and one constant (σ the Stefan-Boltzmann constant). No time derivatives, no PDE, no coupling. Migrated from GasChem.jl@8c12c048 src/radiation_fundamentals.jl:268 (`ClimateSensitivity` @component). The blackbody reference state (F_L = σ·T_e^4) and the analytic differentiation of Stefan-Boltzmann (dF_L/dT_e = 4·σ·T_e^3 → λ_0 = 1 / (4·σ·T_e^3)) together encode the no-feedback Planck response — the only baseline against which feedback-amplified climate sensitivities (water vapor, lapse rate, albedo, cloud) are conventionally reported in IPCC assessments. At Earth's nominal T_e = 255 K the component reproduces the textbook λ_0 ≈ 0.27 K·m^2/W and a CO2-doubling ΔT_e ≈ 1.22 K (S&P Page 105) using a forcing-doubling estimate of 4.6 W/m^2.

Stratospheric ClOx catalytic ozone destruction cycle (Seinfeld & Pandis 2006, Ch. 5 §5.5.1). Migrated from GasChem.jl@8c12c048 src/StratosphericChemistry.jl:272 (`ClOxCycle` @component). Implements 4 ODEs (Cl, ClO, HCl, ClONO2) coupled to 2 algebraic family sums (ClOx = Cl + ClO, Cly = Cl + ClO + HCl + ClONO2). Rate coefficients are Arrhenius (k = A·exp(C/T)) for the five binary reactions and a (T_ref/T)^3.4 form for the termolecular ClO + NO2 + M → ClONO2 channel. All upstream `@constants` are encoded as parameters with their literal SI defaults; physical-condition `@parameters` (T, M, photolysis rates, fixed-bath species O, O3, NO, NO2, OH, CH4) are also parameters so the cycle can be exercised at different atmospheric conditions.

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

CO oxidation chemistry diagnostics from Seinfeld & Pandis (2006) Ch. 6 §6.3 Eqs. 6.9-6.18, pp. 212-219. CO oxidation is the simplest hydrocarbon-oxidation mechanism and illustrates the catalytic HOx cycling that drives tropospheric ozone production (net: CO + 2O₂ + hν → CO₂ + O₃, with OH regenerated through HO₂ + NO). This observed-only algebraic component implements six diagnostic relations: the OH loss rate L_OH (to CO, NO₂, O₃), the HO₂ loss rate L_HO2 (to NO, the HO₂ self-reaction, and O₃), the HOx radical-termination loss rate L_HOx (OH+NO₂→HNO₃ plus the HO₂ self-reaction), the high-NOx HO₂ steady-state concentration HO2_ss (Eq. 6.18), the net ozone production rate P_O3 (HO₂+NO production minus the OH+O₃ and HO₂+O₃ loss channels), and the HOx chain length (propagation rate over termination rate — the number of OH-HO₂ cycles before radical termination). Observed-only algebraic system (no time derivatives): twelve variables (six inputs CO/OH/HO₂/NO/NO₂/O₃ encoded as parameters, six outputs L_OH/L_HO2/L_HOx/HO2_ss/P_O3/chain_length as state), six rate-constant parameters (k_CO_OH, k_HO2_NO, k_HO2_HO2, k_OH_NO2, k_HO2_O3, k_OH_O3), one dimensionless stoichiometric constant (two), and six algebraic equations. Migrated from GasChem.jl@8c12c048 src/co_oxidation.jl:88 (`COOxidation` @component).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

=== MIGRATION NOTES (mdl-09u) ===

GEOS-Chem fullchem gas-phase mechanism (~819 reactions, ~272 species). Migrated from GasChem.jl GEOSChemGasPhase via mtk2esm with sub-system rate-law inlining.

Greenhouse-gas radiative forcing budget for the well-mixed industrial-era GHGs plus tropospheric ozone (Seinfeld & Pandis 2006 Ch. 23 §23.3, p. 1038-1042, IPCC TAR 2001 baseline reproduced in S&P Figure 23.6 / Table 23.4). The component aggregates the five canonical anthropogenic radiative-forcing channels — CO₂, CH₄, N₂O, tropospheric O₃, and the halocarbon family — and exposes per-channel and total radiative forcing as observable outputs. Each channel is parameterized as a dimensionless scaling factor f_X applied to a fixed IPCC TAR reference forcing ΔF_X_ref: ΔF_X = f_X · ΔF_X_ref. The total ΔF_total = Σ ΔF_X is the headline anthropogenic radiative-forcing diagnostic. Observed-only algebraic component: six equations on six state variables (ΔF_CO2, ΔF_CH4, ΔF_N2O, ΔF_O3, ΔF_halo, ΔF_total) driven by five scaling-factor parameters (f_CO2, f_CH4, f_N2O, f_O3, f_halo) and five reference-forcing constants (ΔF_CO2_ref = 1.46, ΔF_CH4_ref = 0.48, ΔF_N2O_ref = 0.15, ΔF_O3_trop_ref = 0.4, ΔF_halo_ref = 0.34, all in W/m^2). No time derivatives, no PDE, no coupling. Migrated from GasChem.jl@8c12c048 src/climate_forcing.jl:104 (`GHGForcing` @component). The scaling-factor design lets a downstream consumer adjust each individual channel without forking the component — useful for (i) reproducing the IPCC AR4/AR5/AR6 revisions to the industrial-era forcing values (e.g., AR5 CO₂ ≈ 1.82 W/m² vs TAR 1.46), (ii) sensitivity studies that probe each channel's contribution to the total, and (iii) attribution scenarios that zero out individual channels (f_X = 0 ⇒ ΔF_X = 0). At the defaults (all f_X = 1), ΔF_total = 1.46 + 0.48 + 0.15 + 0.4 + 0.34 = 2.83 W/m² which matches the upstream IPCC TAR 2001 industrial-era forcing total (S&P p. 1039, sum of the five well-mixed-GHG + O3 channels excluding aerosols).

Global Warming Potential (GWP) for atmospheric trace species with first-order exponential-decay perturbation lifetimes (Seinfeld & Pandis 2006 Ch. 23, Eqs. 23.5-23.6 and Problem 23.3, p. 1050). The GWP is defined as the ratio of the time-integrated radiative forcing from a pulse emission of 1 kg of species A to that of 1 kg of CO₂ over a specified time horizon t_f. For species whose atmospheric perturbation decays exponentially as exp(-t/τ_A), the time-integrated forcing reduces to the closed-form expression τ_A · (1 - exp(-t_f/τ_A)), so the GWP becomes GWP = a_A · τ_A · (1 - exp(-t_f/τ_A)) / [a_CO2 · τ_CO2 · (1 - exp(-t_f/τ_CO2))]. The component is observed-only: five algebraic equations on five state variables (decay_integral_A, decay_integral_CO2, AGWP_A, AGWP_CO2, GWP) driven by three input parameters (τ_A the species lifetime, a_A the radiative efficiency relative to CO₂, t_f the time horizon) and two CO₂-reference constants (τ_CO2 the effective CO₂ lifetime, a_CO2 the reference radiative efficiency). No time derivatives, no PDE, no coupling. Migrated from GasChem.jl@280ee50f src/climate_forcing.jl:182 (`GlobalWarmingPotential` @component). The GWP framework is the IPCC standard for comparing the climate impact of different greenhouse gases on a common (CO₂-equivalent) scale and underlies the conversion between mass emissions of CH₄, N₂O, halocarbons, and other well-mixed GHGs to their CO₂-equivalent emissions for policy and inventory accounting. Canonical GWP₁₀₀ values (IPCC AR4 Table 23.1, S&P p. 1042): CH₄ ≈ 23, N₂O ≈ 296, SF₆ ≈ 22800 — the framework's three-order-of-magnitude span anchors the design choice of representing GWP as a derived ratio rather than a hardcoded table.

Stratospheric HOx catalytic ozone destruction cycle (Seinfeld & Pandis 2006 Ch. 5, §5.4, Eqs. 5.23-5.28). Two-state ODE on the radicals OH and HO2 driven by reactions with O3, atomic O, and NO; HOx = OH + HO2 is exactly conserved by construction (D(OH) + D(HO2) ≡ 0). Migrated from GasChem.jl@8c12c048 src/StratosphericChemistry.jl:187 (`HOxCycle` @component). All rate coefficients are temperature-dependent Arrhenius forms k_X = k_X_A · exp(C_X / T) with the Seinfeld & Pandis bimolecular CGS pre-factors converted to SI via the cm³/molec/s × 1e-6 → m³/s factor; SI rates and SI number-density concentrations (m^-3) are preserved verbatim from upstream.

Methane oxidation reaction-rate diagnostics from Seinfeld & Pandis (2006) Ch. 6 §6.4, Table 6.1, pp. 219-227. Methane oxidation is the archetypal VOC oxidation mechanism in the troposphere, proceeding CH₄ → CH₃O₂ → CH₃O → HCHO → HCO → CO → CO₂. This observed-only algebraic component computes the 17 individual reaction rates R1-R17 of the complete Table 6.1 mechanism (10 bimolecular, 3 termolecular, 4 photolysis reactions) plus three diagnostic aggregates: the gross ozone production rate P_O3_gross = R15 + R3 (the two peroxy-radical + NO channels), the formaldehyde production rate P_HCHO = R6 + R8, and the methane loss rate L_CH4 = R1. Each reaction rate is the product of a 298 K rate constant and the reactant concentrations (R = k·[A]·[B] bimolecular, k·[M]·[A]·[B] termolecular, j·[A] photolysis). The fate of the methylperoxy radical CH₃O₂ — the O₃-producing NO channel R3 versus the chain-terminating HO₂ channel R4 — sets the ozone yield per CH₄ oxidized and is the central NOx-regime diagnostic of the mechanism. Purely algebraic (no time derivatives): 52 variables (15 input species and 17 rate constants encoded as parameters, 20 output diagnostics as state) and 20 equations. Migrated from GasChem.jl@8c12c048 src/methane_oxidation.jl:77 (`MethaneOxidation` @component).

Full time-resolved ODE system for the methane oxidation mechanism in the polluted-continental troposphere (Seinfeld & Pandis 2006 Ch. 6 §6.4 Table 6.1, pp. 219-227). Eighteen-state stiff ODE on the methane oxidation chain CH₄ → CH₃ → CH₃O₂ → CH₃O → HCHO → HCO → CO → (CO₂) plus the supporting NOx/HOx radical chemistry that recycles OH and converts NO ↔ NO₂. The reaction network has 22 reactions: the 17 canonical Table 6.1 reactions covering the Cl-skeleton oxidation chain through HCHO and ozone-formation chemistry via the peroxy + NO channels, plus 5 auxiliary reactions (CO + OH, OH + NO₂ → HNO₃ termination, HO₂ + HO₂ → H₂O₂ termination, NO + O₃ titration, and a zero-order external OH source representing primary OH production from O(¹D) + H₂O that is implicit in the upstream model). Eight termolecular reactions (R2, R6, R13, R14, R17) and the bimolecular cross-reactions have their O₂ and M dependence folded into effective rate constants k6_eff, k13_eff and the explicit k2_0·M·O₂, k14_0·M·O₂, k17_0·M·O₂ products with M_fixed, O2_fixed parameters at fixed STP-tropospheric values (M = 2.5e25 m⁻³, O₂ = 5.25e24 m⁻³). Migrated from GasChem.jl@8c12c048 src/methane_oxidation.jl:213 (`MethaneOxidationODE` @component / @network_component → Catalyst.ode_model). The reaction-network DSL form upstream is converted to explicit ODE equations here because the migration tracker classifies this as `Model` with `variables, parameters, equations` features (not a ReactionSystem-shaped migration — those go to a separate path; see sibling superfast.esm).

Combined atmospheric lifetime from parallel removal pathways — Seinfeld & Pandis (2006) Ch. 2 (Atmospheric Trace Constituents), Eqs. 2.7-2.9. When a trace species is removed by two independent first-order processes acting simultaneously (rate constants k_1 and k_2), the removal rates add: the inverse lifetimes (1/τ) sum while the lifetimes themselves combine harmonically. This observed-only algebraic component implements four relations: the two individual pathway lifetimes tau_1 = 1/k_1 and tau_2 = 1/k_2 (Eq. 2.6 applied per pathway), the summed inverse lifetime inverse_tau = k_1 + k_2 = 1/tau_1 + 1/tau_2 (Eqs. 2.7-2.8), and the combined lifetime tau_combined = (tau_1·tau_2)/(tau_1+tau_2) = 1/(k_1+k_2) (Eq. 2.9). The combined lifetime is always shorter than either individual pathway lifetime, and the faster (shorter-lifetime) pathway dominates: a fast removal process sets the overall atmospheric lifetime even when a slow pathway is also present; when the two pathways are equal the combined lifetime is exactly half of either. Observed-only algebraic system (no time derivatives): four state variables (tau_1, tau_2, tau_combined in s; inverse_tau in s⁻¹) computed from two rate-constant parameters (k_1, k_2 in s⁻¹) by four algebraic equations. Migrated from GasChem.jl@280ee50f src/AtmosphericLifetime.jl:204 (`MultipleRemovalLifetime` @component).

Stratospheric NOx catalytic ozone destruction cycle (Seinfeld & Pandis 2006 Ch. 5 §5.3.2, Eqs. 5.20-5.22). Two-state ODE on the NOx radicals NO and NO2 driven by reactions with O3 and atomic O, plus daytime NO2 photolysis; NOx = NO + NO2 is exactly conserved by construction (D(NO) + D(NO2) ≡ 0). Migrated from GasChem.jl@8c12c048 src/StratosphericChemistry.jl:118 (`NOxCycle` @component). Rate coefficients are temperature-dependent Arrhenius forms k_X = k_X_A · exp(C_X / T) with the Seinfeld & Pandis bimolecular CGS pre-factors converted to SI via the cm³/molec/s × 1e-6 → m³/s factor; SI rates and SI number-density concentrations (m^-3) preserved verbatim from upstream.

The NOx (NO + NO₂) photochemical cycle that governs tropospheric ozone — Seinfeld & Pandis (2006) Ch. 6 §6.2, Eqs. 6.5-6.8, pp. 207-212. During daytime three reactions cycle rapidly between NO, NO₂ and O₃: NO₂ + hν → NO + O (λ < 424 nm), O + O₂ + M → O₃ + M, and NO + O₃ → NO₂ + O₂. In the absence of other oxidants this cycle reaches a photostationary state (the Leighton relationship). Implements four algebraic diagnostic relations: (Eq. 6.5) ground-state O-atom steady-state concentration O = j_NO2·[NO₂] / (k_O_O2_M·[O₂]·[M]), (Eq. 6.6) photostationary-state ozone O3_pss = j_NO2·[NO₂] / (k_NO_O3·[NO]) — the Leighton relationship, (Eq. 6.7) the photostationary-state parameter Φ = j_NO2·[NO₂] / (k_NO_O3·[NO]·[O₃]) which is 1 at exact PSS and deviates when peroxy radicals perturb the cycle, and (Eq. 6.8) the net ozone production rate P_O3 = j_NO2·[NO₂] − k_NO_O3·[NO]·[O₃]. Observed-only algebraic system (no time derivatives): nine variables (five inputs NO/NO2/O3/O2/M encoded as parameters, four outputs O/O3_pss/Φ/P_O3 encoded as state) plus three rate-constant parameters (j_NO2, k_O_O2_M, k_NO_O3). Migrated from GasChem.jl@8c12c048 src/nox_photochemistry.jl:88 (`NOxPhotochemistry` @component). Sibling component PhotostationaryState (src/nox_photochemistry.jl:145) migrates separately to photostationary.esm.

Tropospheric OH radical production from O₃ photolysis — Seinfeld & Pandis (2006) Ch. 6 §6.1 Eqs. 6.1, 6.3, 6.4, pp. 204-207. The dominant source of OH in the troposphere is O₃ photolysis below 320 nm producing electronically excited O(¹D), which either reacts with H₂O to yield two OH radicals or is collisionally quenched back to ground-state O(³P) by N₂/O₂. Implements three algebraic relations: (Eq. 6.1) O(¹D) steady-state concentration [O(¹D)] = j_O₃·[O₃] / (k₃[M] + k₄[H₂O]), (Eq. 6.4) OH yield ε_OH = 2·k₄[H₂O] / (k₃[M] + k₄[H₂O]) as the fraction of O(¹D) producing OH (the factor of 2 accounts for the 2 OH produced per O(¹D)+H₂O encounter — ε_OH ranges 0..2), (Eq. 6.3) OH production rate P_OH = j_O₃·[O₃]·ε_OH. The effective quenching rate k₃_eff = f_N₂·k₃,N₂ + f_O₂·k₃,O₂ is the air-composition-weighted average of the N₂ and O₂ quenching channels. Observed-only algebraic system (no time derivatives): six variables (three inputs O₃/H₂O/M as parameters, three outputs O₁D/ε_OH/P_OH as state) plus six rate-parameter inputs (j_O₃, k₃_N₂, k₃_O₂, k₄, f_N₂, f_O₂) and one stoichiometric constant (two=2). Migrated from GasChem.jl@8c12c048 src/oh_production.jl:88 (`OHProduction` @component).

Atmospheric lifetime against reaction with the hydroxyl radical (OH), from Seinfeld & Pandis (2006) Atmospheric Chemistry and Physics Ch. 2, Eq. 2.12: tau = 1/(k_OH*[OH]). OH is the dominant daytime oxidant of the troposphere, so the OH-reaction lifetime sets how long most reactive trace gases — methane, carbon monoxide, non-methane VOCs — persist in the atmosphere. This observed-only algebraic component implements two relations: an effective pseudo-first-order loss rate constant k_eff = k_OH*OH_conc (the second-order reaction X + OH collapsed onto the approximately constant ambient OH), and the lifetime tau_OH = 1/k_eff. The lifetime is jointly controlled by the species' intrinsic reactivity (k_OH, spanning four-plus decades across tropospheric trace gases) and the ambient oxidising capacity ([OH], varying with season, latitude and pollution): a species may persist for years in clean remote air and only hours in a polluted daytime plume. Purely algebraic system (no time derivatives): four variables — one parameter k_OH, one input OH_conc encoded as a parameter, two outputs k_eff and tau_OH as state — and two equations. Migrated from GasChem.jl@280ee50f src/AtmosphericLifetime.jl:264 (`OHReactionLifetime` @component).

Ozone Production Efficiency (OPE) diagnostic from Seinfeld & Pandis (2006) Ch. 6 §6.3 Eqs. 6.21-6.24, pp. 212-219. OPE = Δ[O₃]/Δ[NOx] is the number of ozone molecules produced per molecule of NOx consumed — a central diagnostic for the NOx-VOC-O₃ regime structure of tropospheric photochemistry. This observed-only algebraic component implements three relations: gross ozone production rate P_O3 = k_HO2_NO·[HO₂]·[NO] + k_RO2_NO·[RO₂]·[NO] (the two peroxy-radical + NO channels — each peroxy+NO reaction makes an NO₂ whose photolysis yields an O₃), NOx loss rate L_NOx = k_OH_NO2·[OH]·[NO₂] (the OH + NO₂ + M → HNO₃ termination, the dominant daytime NOx sink), and OPE = P_O3 / L_NOx. High OPE (low-NOx, NOx-limited regime) means each NOx molecule cycles through many O₃-producing reactions before it is lost as nitric acid; low OPE (high-NOx, VOC-limited regime) means NOx is removed before it can drive much O₃ production. Observed-only algebraic system (no time derivatives): eight variables (five inputs OH/HO₂/RO₂/NO/NO₂ encoded as parameters, three outputs P_O3/L_NOx/OPE as state) plus three rate-constant parameters (k_HO2_NO, k_RO2_NO, k_OH_NO2) and three algebraic equations. Migrated from GasChem.jl@280ee50f src/co_oxidation.jl:183 (`OzoneProductionEfficiency` @component).

Photon energy equation (Seinfeld & Pandis 2006 Ch. 4, Eq. 4.1) — the energy Δε and frequency ν of a photon as a function of wavelength λ via Planck's constant h and the speed of light c: ν = c/λ and Δε = hν, equivalently the chained form Δε = hc/λ. The component is observed-only: two algebraic equations on two state variables (Δε the photon energy in J and ν the frequency in Hz) driven by one input parameter (λ the wavelength) and two constants (h Planck's constant and c the speed of light). No time derivatives, no PDE, no coupling. Migrated from GasChem.jl@8c12c048 src/radiation_fundamentals.jl:25 (`PhotonEnergy` @component). The photon energy equation is the foundational quantum-radiative bridge that maps continuous-wave radiation to the discrete photon picture: paired with the Planck spectral distribution (BlackbodyRadiation), Stefan-Boltzmann total flux (StefanBoltzmann), and Wien peak displacement (WienDisplacement), it lets a radiative-transfer model convert spectral irradiance to photon fluxes and back — the quantity needed for actinic-flux / photolysis-rate calculations that drive atmospheric photochemistry (e.g., O2 + hν → 2 O at ~242 nm and O3 + hν → O + O2 at ~310 nm, the two Chapman-cycle photolysis channels). The defaults (λ = 500 nm) give ν ≈ 600 THz and Δε ≈ 3.97e-19 J ≈ 2.48 eV — visible green light, the canonical solar-peak wavelength matching Wien's law applied to T_sun ≈ 5800 K.

Photostationary-state diagnostic for the NO-NO₂-O₃ Leighton cycle — Seinfeld & Pandis (2006) Ch. 6 §6.2, Eqs. 6.6-6.7, pp. 207-212. Computes the photostationary-state parameter Φ = j_NO2·[NO₂] / (k_NO+O₃·[NO]·[O₃]) and its deviation from unity Φ_deviation = Φ - 1. Φ = 1 is the exact Leighton photostationary state (pure NO-NO₂-O₃ cycling, zero net ozone production); Φ > 1 indicates additional oxidants (peroxy radicals HO₂/RO₂ converting NO→NO₂ and producing ozone), Φ < 1 indicates net ozone loss. This observed-only algebraic component is the simplified companion to NOxPhotochemistry (the full Eqs. 6.5-6.8 diagnostic): five variables (three inputs NO/NO₂/O₃ encoded as parameters, two outputs Φ/Φ_deviation as state), two rate parameters (j_NO2, k_NO_O3) plus the dimensionless unity constant `one`, and two algebraic equations. No time derivatives. Migrated from GasChem.jl@8c12c048 src/nox_photochemistry.jl:145 (`PhotostationaryState` @component).

Planetary equilibrium temperature from the top-of-atmosphere energy balance (Seinfeld & Pandis 2006 Ch. 4 Eqs. 4.5-4.7). The absorbed solar flux F_S = S_0/4 * (1 - R_p), the emitted longwave flux F_L = sigma * T_e^4 (Stefan-Boltzmann law), and at equilibrium F_S = F_L. Solving the constraint gives T_e = (S_0/4 * (1-R_p) / sigma)^(1/4). At canonical Earth values (S_0 = 1370 W/m^2, R_p = 0.3), F_S = F_L = 239.75 W/m^2 and T_e = 255 K (S&P p. 101). Migrated from GasChem.jl@8c12c048 src/radiation_fundamentals.jl:211 (`PlanetaryEnergyBalance` @component).

POLLU air-pollution photochemistry mechanism from GasChem.jl. 20 species and 25 reactions (15 thermal + 10 photolytic) describing tropospheric NOx / odd-oxygen / hydrocarbon / sulfur chemistry. Introduced by Verwer (1994) as a stiff-ODE benchmark for chemical-kinetics integrators and widely used since as a standard stiff test problem. Hand-translated from the upstream Catalyst @reaction_network in GasChem.jl src/Pollu.jl: 25 rate constants carried verbatim as parameters, 20 species with their declared reservoir defaults, and 25 mass-action reactions numbered R1..R25 in the canonical POLLU order. All reaction rates are bare parameter references and all substrate stoichiometries are 1, so the serialized mass-action system matches the upstream combinatoric_ratelaws=false ReactionSystem exactly.

Composed radiation-fundamentals system from Seinfeld & Pandis (2006) Chapter 4 (Eqs. 4.1-4.11). A pure structural aggregation (no coupling equations) of seven independent components: PhotonEnergy (photon energy-frequency-wavelength relations, Eq. 4.1), BlackbodyRadiation (Planck's law, Eq. 4.2), WienDisplacement (peak emission wavelength, Eq. 4.3), StefanBoltzmann (total emissive power, Eq. 4.4), PlanetaryEnergyBalance (Earth's equilibrium temperature, Eqs. 4.5-4.7), ClimateSensitivity (temperature response to forcing, Eqs. 4.8-4.10), and TOARadiativeForcing (net top-of-atmosphere flux, Eq. 4.11). Each component is inlined as a named subsystem; variables are dot-namespaced (RadiationFundamentals.<subsystem>.<var>). Migrated from GasChem.jl@8c12c048 src/radiation_fundamentals.jl:367 (`RadiationFundamentals` @component).

The RADM2 gas-phase mechanism (Stockwell et al. 1990) exactly as WRF-Chem chem_opt = 101 (the KPP build of RADM2; chem_opt = 1 is the older hand-coded RADM2 of chem/module_radm.F, a different code path) integrates it: the 156 reactions of radm2.eqn (21 photolysis + 135 thermal) over 59 variable species, translated from chem/KPP/mechanisms/radm2/radm2.eqn and radm2.spc of WRF v4.8.0 by a translation script. The reaction system has 157 entries, one more than the .eqn, because the negative product "-0.9 OH" of reaction 60 is written as the extra entry R060x. The document holds three components. The model RADM2RateConstants evaluates every thermal rate coefficient from the hand-authored WRF rate-law templates (radm2_ratelaws.esm) with the .eqn coefficients bound once, and exposes them as observeds tested at t = 0 against the real64 KPP box driver and against a real WRF-Chem chem_opt = 101 single-column run. The reaction system RADM2 carries the stoichiometry only, each rate being a scoped reference to that model (photolysis rates are its parameters j_*). The model RADM2Tendencies exposes the mass-action tendency of every species as an observed, so the right-hand side is tested at t = 0 independently of any integrator. Species are in molec/cm^3 (the KPP units; WRF converts its ppmV chem array with conv = 1e-6 dens2con_a rho). The two KPP fixed species are not species here: air (M) and water vapour (H2O) are the parameters RADM2RateConstants.M and RADM2RateConstants.H2O, the single source of each for the whole document. The rate laws read them as arguments, the five reactions in which KPP multiplies by a fixed species (R022, R024 and R036 by M; R025 and R033 by H2O) multiply their rate by them, and the relative humidity of the heterogeneous N2O5 rate is derived from H2O, M, T and p with WRF's own formula, so no override can leave two copies of one quantity disagreeing. Mass action is that of esm-spec 7.4, v = k prod S_i^n_i with no 1/n_i! factor, which is also what KPP generates. The eight reactions with a doubled substrate (R032 and R033 HO2 + HO2, R036 NO + NO, R119 MO2 + MO2, R140 ACO3 + ACO3, R147 XO2 + XO2, R153 XNO2 + XNO2, R156 OLN + OLN) carry their .eqn coefficients unchanged on that understanding: a binding that lowers this document to Catalyst.jl must build it with combinatoric_ratelaws = false, or those eight rates come out at half the KPP value. Single-precision literals of radm2.eqn and of the WRF-Chem coupler (.20946e0, .78084, -2.3, the constants of rc_n2o5 and of the relative humidity) are transcribed as the binary64 value of the single-precision number, since that is what the Fortran evaluates.

The RADM2 gas-phase mechanism (Stockwell et al. 1990) exactly as WRF-Chem chem_opt = 101 (the KPP build of RADM2; chem_opt = 1 is the older hand-coded RADM2 of chem/module_radm.F, a different code path) integrates it: the 156 reactions of radm2.eqn (21 photolysis + 135 thermal) over 59 variable species, translated from chem/KPP/mechanisms/radm2/radm2.eqn and radm2.spc of WRF v4.8.0 by a translation script. The reaction system has 157 entries, one more than the .eqn, because the negative product "-0.9 OH" of reaction 60 is written as the extra entry R060x. The document holds three components. The model RADM2RateConstants evaluates every thermal rate coefficient from the hand-authored WRF rate-law templates (radm2_ratelaws.esm) with the .eqn coefficients bound once, and exposes them as observeds tested at t = 0 against the real64 KPP box driver and against a real WRF-Chem chem_opt = 101 single-column run. The reaction system RADM2 carries the stoichiometry only, each rate being a scoped reference to that model (photolysis rates are its parameters j_*). The model RADM2Tendencies exposes the mass-action tendency of every species as an observed, so the right-hand side is tested at t = 0 independently of any integrator. Species are in molec/cm^3 (the KPP units; WRF converts its ppmV chem array with conv = 1e-6 dens2con_a rho). The two KPP fixed species are not species here: air (M) and water vapour (H2O) are the parameters RADM2RateConstants.M and RADM2RateConstants.H2O, the single source of each for the whole document. The rate laws read them as arguments, the five reactions in which KPP multiplies by a fixed species (R022, R024 and R036 by M; R025 and R033 by H2O) multiply their rate by them, and the relative humidity of the heterogeneous N2O5 rate is derived from H2O, M, T and p with WRF's own formula, so no override can leave two copies of one quantity disagreeing. Mass action is that of esm-spec 7.4, v = k prod S_i^n_i with no 1/n_i! factor, which is also what KPP generates. The eight reactions with a doubled substrate (R032 and R033 HO2 + HO2, R036 NO + NO, R119 MO2 + MO2, R140 ACO3 + ACO3, R147 XO2 + XO2, R153 XNO2 + XNO2, R156 OLN + OLN) carry their .eqn coefficients unchanged on that understanding: a binding that lowers this document to Catalyst.jl must build it with combinatoric_ratelaws = false, or those eight rates come out at half the KPP value. Single-precision literals of radm2.eqn and of the WRF-Chem coupler (.20946e0, .78084, -2.3, the constants of rc_n2o5 and of the relative humidity) are transcribed as the binary64 value of the single-precision number, since that is what the Fortran evaluates.

The RADM2 gas-phase mechanism (Stockwell et al. 1990) exactly as WRF-Chem chem_opt = 101 (the KPP build of RADM2; chem_opt = 1 is the older hand-coded RADM2 of chem/module_radm.F, a different code path) integrates it: the 156 reactions of radm2.eqn (21 photolysis + 135 thermal) over 59 variable species, translated from chem/KPP/mechanisms/radm2/radm2.eqn and radm2.spc of WRF v4.8.0 by a translation script. The reaction system has 157 entries, one more than the .eqn, because the negative product "-0.9 OH" of reaction 60 is written as the extra entry R060x. The document holds three components. The model RADM2RateConstants evaluates every thermal rate coefficient from the hand-authored WRF rate-law templates (radm2_ratelaws.esm) with the .eqn coefficients bound once, and exposes them as observeds tested at t = 0 against the real64 KPP box driver and against a real WRF-Chem chem_opt = 101 single-column run. The reaction system RADM2 carries the stoichiometry only, each rate being a scoped reference to that model (photolysis rates are its parameters j_*). The model RADM2Tendencies exposes the mass-action tendency of every species as an observed, so the right-hand side is tested at t = 0 independently of any integrator. Species are in molec/cm^3 (the KPP units; WRF converts its ppmV chem array with conv = 1e-6 dens2con_a rho). The two KPP fixed species are not species here: air (M) and water vapour (H2O) are the parameters RADM2RateConstants.M and RADM2RateConstants.H2O, the single source of each for the whole document. The rate laws read them as arguments, the five reactions in which KPP multiplies by a fixed species (R022, R024 and R036 by M; R025 and R033 by H2O) multiply their rate by them, and the relative humidity of the heterogeneous N2O5 rate is derived from H2O, M, T and p with WRF's own formula, so no override can leave two copies of one quantity disagreeing. Mass action is that of esm-spec 7.4, v = k prod S_i^n_i with no 1/n_i! factor, which is also what KPP generates. The eight reactions with a doubled substrate (R032 and R033 HO2 + HO2, R036 NO + NO, R119 MO2 + MO2, R140 ACO3 + ACO3, R147 XO2 + XO2, R153 XNO2 + XNO2, R156 OLN + OLN) carry their .eqn coefficients unchanged on that understanding: a binding that lowers this document to Catalyst.jl must build it with combinatoric_ratelaws = false, or those eight rates come out at half the KPP value. Single-precision literals of radm2.eqn and of the WRF-Chem coupler (.20946e0, .78084, -2.3, the constants of rc_n2o5 and of the relative humidity) are transcribed as the binary64 value of the single-precision number, since that is what the Fortran evaluates.

The five SuperFast rate-law helper functions migrated from GasChem.jl@8c12c048482b515fb8eb2110bf8ab4b4f4e71309 src/SuperFast.jl — the reusable builder functions the SuperFast() chemical mechanism uses to construct the rate coefficient of every gas-phase reaction. Each is migrated as its own observed-only algebraic `models` entry: rate_toppb (SuperFast.jl:6) the constant-rate / `constant_k` converter, arrh (:33) the modified-Arrhenius workhorse, arr_3rd (:64) the third-body / Troe-falloff law, rate_2HO2 (:102) the HO2+HO2 law with water-vapour enhancement, and rate_OH_CO (:142) the JPL 15-10 OH+CO law. Upstream each function returns a one-variable ReactionSystem (`@variables k(t)`); the composed builders (arr_3rd, rate_2HO2, rate_OH_CO) compose `arrh` sub-systems. This file reproduces each function's compiled rate as a topologically-ordered cascade of `type: state` algebraic equations whose named intermediates mirror the upstream Julia locals and sub-system k's verbatim, with the Arrhenius coefficients exposed as `type: parameter` (defaults taken from the representative SuperFast reaction each builder serves). All five models are purely algebraic — no time derivatives — so each rate coefficient is constant in time. Units follow the upstream's mixed CGS / ppb system (rate coefficients in 1/(s*ppb), Arrhenius pre-exponentials in cm^3/molec/s).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

The five SuperFast rate-law helper functions migrated from GasChem.jl@8c12c048482b515fb8eb2110bf8ab4b4f4e71309 src/SuperFast.jl — the reusable builder functions the SuperFast() chemical mechanism uses to construct the rate coefficient of every gas-phase reaction. Each is migrated as its own observed-only algebraic `models` entry: rate_toppb (SuperFast.jl:6) the constant-rate / `constant_k` converter, arrh (:33) the modified-Arrhenius workhorse, arr_3rd (:64) the third-body / Troe-falloff law, rate_2HO2 (:102) the HO2+HO2 law with water-vapour enhancement, and rate_OH_CO (:142) the JPL 15-10 OH+CO law. Upstream each function returns a one-variable ReactionSystem (`@variables k(t)`); the composed builders (arr_3rd, rate_2HO2, rate_OH_CO) compose `arrh` sub-systems. This file reproduces each function's compiled rate as a topologically-ordered cascade of `type: state` algebraic equations whose named intermediates mirror the upstream Julia locals and sub-system k's verbatim, with the Arrhenius coefficients exposed as `type: parameter` (defaults taken from the representative SuperFast reaction each builder serves). All five models are purely algebraic — no time derivatives — so each rate coefficient is constant in time. Units follow the upstream's mixed CGS / ppb system (rate coefficients in 1/(s*ppb), Arrhenius pre-exponentials in cm^3/molec/s).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

The five SuperFast rate-law helper functions migrated from GasChem.jl@8c12c048482b515fb8eb2110bf8ab4b4f4e71309 src/SuperFast.jl — the reusable builder functions the SuperFast() chemical mechanism uses to construct the rate coefficient of every gas-phase reaction. Each is migrated as its own observed-only algebraic `models` entry: rate_toppb (SuperFast.jl:6) the constant-rate / `constant_k` converter, arrh (:33) the modified-Arrhenius workhorse, arr_3rd (:64) the third-body / Troe-falloff law, rate_2HO2 (:102) the HO2+HO2 law with water-vapour enhancement, and rate_OH_CO (:142) the JPL 15-10 OH+CO law. Upstream each function returns a one-variable ReactionSystem (`@variables k(t)`); the composed builders (arr_3rd, rate_2HO2, rate_OH_CO) compose `arrh` sub-systems. This file reproduces each function's compiled rate as a topologically-ordered cascade of `type: state` algebraic equations whose named intermediates mirror the upstream Julia locals and sub-system k's verbatim, with the Arrhenius coefficients exposed as `type: parameter` (defaults taken from the representative SuperFast reaction each builder serves). All five models are purely algebraic — no time derivatives — so each rate coefficient is constant in time. Units follow the upstream's mixed CGS / ppb system (rate coefficients in 1/(s*ppb), Arrhenius pre-exponentials in cm^3/molec/s).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

Parameters-preset model representing typical remote/background tropospheric conditions with low NOx. Migrated from GasChem.jl@8c12c048 src/combined_system.jl:261 (`RemoteConditions` @component). Eleven species concentrations are declared as parameters in SI units (m⁻³); the model exposes them as algebraic outputs (`*_out`) so a parent system or test harness can read presets without depending on MTK parameter-introspection APIs. Based on Seinfeld & Pandis Chapter 6 background conditions: ~30 ppb O₃, ~10 ppt NO, ~20 ppt NO₂, ~80 ppb CO.

Atmospheric-lifetime calculator for a trace species, from Seinfeld & Pandis (2006) Ch. 2 (Atmospheric Trace Constituents), Eqs. 2.3-2.6. The component is observed-only: four algebraic equations, no time derivative, expressing the four textbook definitions of atmospheric lifetime as functions of the species burden Q and the removal/production/outflow rates. tau_general = Q/(R_removal + F_out) is the general lifetime accounting for both chemical removal R_removal and outflow F_out to other reservoirs (Eq. 2.3); tau_removal = Q/R_removal is the global-atmosphere limit with no outflow (Eq. 2.4); tau_production = Q/P is the production-based lifetime, equal to tau_removal at steady state (Eq. 2.5); and tau_first_order = 1/lambda is the lifetime when removal follows first-order kinetics R_removal = lambda*Q (Eq. 2.6). The four definitions interlock: Eq. 2.3 reduces to Eq. 2.4 as F_out -> 0, Eqs. 2.4 and 2.5 coincide when production balances removal, and Eq. 2.6 coincides with Eq. 2.4 when lambda is the consistent first-order rate constant R_removal/Q. Migrated from GasChem.jl@280ee50f src/AtmosphericLifetime.jl:132 (`SpeciesLifetime` @component). Every equation is a closed-form algebraic expression in the parameters, so every inline-test expected value below is the exact arithmetic evaluation of the textbook formula.

Stefan-Boltzmann law for blackbody radiation — Seinfeld & Pandis (2006) Ch. 4 Eq. 4.4. Total emissive power F_B of a blackbody at temperature T integrated over all wavelengths: F_B = σ·T^4, where σ = 5.671×10⁻⁸ W·m⁻²·K⁻⁴. Migrated from GasChem.jl@8c12c048 src/radiation_fundamentals.jl:164 (`StefanBoltzmann` @component). One observed binding (F_B) over two parameters (T input + σ as a fixed-default parameter encoding the upstream `@constants` block per the rig convention of translating `@constants` to fixed-default parameters so units flow through MTK's unit checker — matches sibling clmu_atmosphere.esm/surface_energy_flux.esm). Closed-form algebraic: after mtkcompile the system has zero ODE states and the inline-test runner exercises F_B at its observed algebraic value.

Comprehensive stratospheric ozone chemistry (Seinfeld & Pandis 2006, Chapter 5) — a monolithic 15-state ODE plus 5 algebraic family sums combining the Chapman mechanism, O(1D) photochemistry, the N2O NOx source, and the NOx / HOx / ClOx / BrOx catalytic ozone-destruction cycles. Migrated from GasChem.jl@8c12c048 src/StratosphericChemistry.jl:497. SI units throughout.

SuperFast gas-phase atmospheric chemistry mechanism from GasChem.jl. 12 active species + 3 quasi-constant reservoirs (O2/CH4/H2O; constant=true per ESS gt-ertm), 27 reactions covering tropospheric ozone chemistry. Regenerated from the upstream MTK ReactionSystem via mtk2esm (ESS gt-dod2). Fractional stoichiometries preserved directly (ESS gt-1e96); rate-law wrappers (arrhenius, third-body falloff, JPL 15-10 OH+CO, H2O-dependent HO2+HO2) inlined as Expression trees.

Operator model that turns first-order dry + wet deposition loss-rate coefficients into additive sink terms on a SuperFast-family gas-phase mechanism. Each equation is D(<X>) ~ -(k_dry + k_wet)*<X> over the model's OWN species unknowns; when this model is merged with a SuperFast reaction system via an `operator_compose` coupling (systems: [<Chem>, SuperFastDepositionSink]), the flattener matches each sink equation's dependent variable to the chemistry system's state of the same species name and sums the two right-hand sides (dc/dt += -k*c), then retires the sink's own declaration of that name (esm-spec 10.1/10.2 — direct match, else the bare-name match). The deposition rate coefficients are exposed as parameters so they can be driven from the full DryDepositionGas (Wesley 1989) and WetDeposition (EMEP) components via param_to_var edges in an assembly. Species->rate mapping mirrors AtmosphericDeposition.jl/ext/GasChemExt.jl couple2(SuperFastCoupler, DryDepositionGasCoupler / WetDepositionCoupler): NO reuses NO2's dry-dep rate; CH2O uses the formaldehyde (HCHO) dry-dep rate; the wet rate k_wet is the lumped soluble-gas WetDeposition.k_othergas applied to HNO3, H2O2, CH2O, CH3OOH.

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

Top-of-atmosphere (TOA) radiative-flux balance for a 0-D planetary climate model, following Seinfeld & Pandis (2006) Chapter 4 Eq. 4.11. Implements the net incoming flux F_net = S_0/4 · (1 - R_p) - F_L as a single algebraic relation between the absorbed shortwave flux F_S = S_0/4 · (1 - R_p) (Eq. 4.5, the spherical-projection factor of 1/4 accounts for the planet receiving solar flux over its cross-section πR² but emitting over its full surface 4πR²) and the outgoing longwave flux F_L (input parameter, typically supplied by the sibling PlanetaryEnergyBalance / StefanBoltzmann components in this domain). Sign convention: positive F_net means the planet is gaining energy (warming); negative F_net means losing energy (cooling). At default parameters (S_0=1370 W/m², R_p=0.3, F_L=239.75 W/m²) the planet is in exact radiative equilibrium (F_net = 0). Migrated from GasChem.jl@8c12c048 src/radiation_fundamentals.jl:327 (`TOARadiativeForcing` @component). Sibling component to PhotonEnergy (Eq. 4.1), BlackbodyRadiation (Eq. 4.2), WienDisplacement (Eq. 4.3), StefanBoltzmann (Eq. 4.4), PlanetaryEnergyBalance (Eqs. 4.5-4.7), ClimateSensitivity (Eqs. 4.8-4.10) — together they compose the upstream RadiationFundamentals (radiation_fundamentals.jl:367) system.

Complete tropospheric mass-budget model for a trace species, from Seinfeld & Pandis (2006) Ch. 2 §2.3, Eqs. 2.13-2.17. A single linear first-order ODE on the species burden Q drives the dynamics: dQ/dt = (P_n + P_a + P_c) - (k_d + k_w + k_c + k_t)·Q — total production from natural emissions, anthropogenic emissions, and in-troposphere chemical production, balanced against first-order removal by dry deposition, wet deposition, chemical loss, and cross-tropopause transport to the stratosphere. The model also reports the algebraic diagnostics that the textbook builds on this budget: the total production rate P_total and removal rate R_total, the total first-order removal rate constant k_total, the per-pathway lifetimes tau_dry/tau_wet/tau_chem/tau_transport = 1/k_X, the total atmospheric lifetime tau_total = 1/k_total (Eq. 2.15), and the production-based lifetime tau_production = Q/P_total (Eqs. 2.16-2.17), which equals tau_total once the burden has relaxed to steady state. Migrated from GasChem.jl@280ee50f src/AtmosphericLifetime.jl:336 (`TroposphericBudget` @component). The system is linear with constant coefficients, so the burden has the exact closed form Q(t) = Q_ss + (Q_0 - Q_ss)·exp(-k_total·t) with steady state Q_ss = P_total/k_total; every inline-test expected value below is that analytic solution.

Combined tropospheric chemistry diagnostic system (Seinfeld & Pandis 2006, Chapter 6) — couples three photochemical subsystems into a comprehensive steady-state diagnostic model of tropospheric photochemistry: OH production from O3 photolysis (§6.1), the NOx photochemical cycle (§6.2), and CO oxidation chemistry (§6.3). Migrated from GasChem.jl@8c12c048 src/combined_system.jl:54 (`TroposphericChemistrySystem` @component). The three subsystems — `oh` (OHProduction), `nox` (NOxPhotochemistry), `co` (COOxidation) — are inlined verbatim (ESS spec §4.7 subsystem composition) from their already-migrated standalone .esm files; the parent supplies 14 coupling equations feeding the shared species (O3, NO, NO2, OH, HO2, CO, CH3O2, H2O, M, O2) into the subsystems and 9 combined-diagnostic equations (total/net O3 production, ozone production efficiency, NOx loss rate, HOx chain length). Purely algebraic — a steady-state diagnostic system with no time derivatives. SI units throughout (m^-3 for concentrations, m^3/s for bimolecular rate constants).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

GEOS-Chem gas-phase reaction rate laws — the 37 rate-coefficient builder functions of GasChem.jl src/geoschem_ratelaws.jl, adapted from the GEOS-Chem KPP/fullchem mechanism (github.com/geoschem/geos-chem, commit 4722f288). Each builder computes a single reaction rate coefficient k from temperature and air number density: constant rates (constant_k, constant_k_1), modified-Arrhenius forms in ppb and SI molecular units (arrhenius_ppb, arrhenius_ppb_3, arrhenius_mlc_SI, arrhenius_mlc_1, arrplus_*, tunplus_*), Troe / third-body pressure-dependent falloff rates (arr_3rdbody, arr_3rdbody_1, rate_OHCO, rate_PAN_abab, rate_PAN_acac, eq_const, eq_const_1), and a family of mechanism-specific rates for HO2, RO2+NO, isoprene, glycolaldehyde, DMS and HNO3 chemistry. Each rate law is migrated as an independent purely-algebraic model: the inputs (T, num_density, Arrhenius coefficients) are parameters, the rate coefficient k is the single state variable defined by one algebraic equation, and an inline test reproduces the rate constant asserted by the corresponding @testitem in GasChem.jl test/geoschem_ratelaws_test.jl (compiled at T=293 K, num_density = 2.7e19 molec/cm^3). The GEOS-Chem license applies (github.com/geoschem/geos-chem/blob/main/LICENSE.txt).

Parameters-preset component that exposes typical lower-troposphere chemical composition (Seinfeld & Pandis 2006, Chapter 6) as observable outputs. Migrated from GasChem.jl@280ee50f src/combined_system.jl:177 (`TypicalConditions` @component). The component declares 11 species concentrations as parameters with fixed default values in SI units (m^-3) for typical mid-latitude lower-tropospheric daytime conditions — total air number density M = 2.5e25 m^-3 at STP, O2 = 5.25e24 m^-3 (21% of M), H2O = 4.0e23 m^-3 (~50% RH at 298 K), O3 = 1.0e18 m^-3 (~40 ppb), NO = 2.5e15 m^-3 (~0.1 ppb), NO2 = 2.5e16 m^-3 (~1 ppb), CO = 2.5e18 m^-3 (~100 ppb), CH4 = 4.5e19 m^-3 (~1800 ppb), OH = 1.0e12 m^-3 (typical daytime), HO2 = 1.0e14 m^-3 (typical daytime), CH3O2 = 1.0e14 m^-3 (typical daytime) — and 11 passthrough algebraic equations of the form `<species>_out ~ <species>` that publish each species parameter on the canonical `<species>_out(t)` observable name. This design exists because the upstream `TroposphericChemistrySystem` consumes species concentrations on the bare names (M, O2, H2O, O3, NO, NO2, OH, HO2, CO, CH4, CH3O2) and a downstream consumer can compose a conditions preset by binding its preset parameters into those input variables — the `_out` suffix makes the conditions component a publishable upstream of any compose graph. Parameterized as observed-only with 11 passthrough/identity equations — no time derivatives, no `@register_symbolic` dependencies, no PDE — matching the upstream `length(equations(sys)) == 11` / `length(unknowns(sys)) == 11` structural shape.

Parameter-preset condition system representing typical urban-air-quality lower-troposphere conditions with elevated NOx, CO, and reduced HOx, following Seinfeld & Pandis (2006) Chapter 6. Migrated from GasChem.jl@8c12c048 src/combined_system.jl:219 (`UrbanConditions` @component). The component declares 11 species number-density parameters (M, O2, H2O, O3, NO, NO2, CO, CH4, OH, HO2, CH3O2) with urban-regime defaults in SI units (m^-3) and 11 corresponding `_out` output state variables, one per parameter, defined by identity equations `*_out ~ *`. The component is a sibling preset to `TypicalConditions` (background-air defaults) and `RemoteConditions` (clean-remote defaults); together they parametrize the three canonical regimes the upstream `TroposphericChemistrySystem` is exercised against. Compared to TypicalConditions: NO is 100x higher (10 vs 0.1 ppb), NO2 is 30x higher (30 vs 1 ppb), CO is 20x higher (2000 vs 100 ppb), and OH/HO2 are reduced 2x (titrated by the elevated NOx and CO oxidation chain). All concentrations are positive number densities at standard temperature and pressure; the `_out` indirection lets downstream consumers wire the preset values into the canonical tropospheric-chemistry input interface without renaming.

Wien's displacement law (Seinfeld & Pandis 2006 Ch. 4, Eq. 4.3) — the peak emission wavelength λ_max of a blackbody at temperature T is given by the simple inverse relation λ_max = b / T where b is Wien's displacement constant (2.897×10⁻³ m·K). The component is observed-only: one algebraic equation on one state variable (λ_max the peak wavelength) driven by one input parameter (T the temperature) and one constant (b the displacement constant). No time derivatives, no PDE, no coupling. Migrated from GasChem.jl@8c12c048 src/radiation_fundamentals.jl:121 (`WienDisplacement` @component). Wien's law is one half of the radiative-transfer toolkit for blackbody emission: paired with the Stefan-Boltzmann law σT⁴ (total emitted power) and the Planck function (spectral distribution), it lets a radiative-transfer model identify which spectral region a body's emission concentrates in. The 5800 K Sun peaks at ~500 nm (visible green); the 255 K Earth peaks at ~10 μm (thermal infrared); the 3 K cosmic microwave background peaks at ~1 mm (microwave). The temperature-inverse scaling means hotter sources emit at shorter wavelengths — the canonical fact behind the visible spectrum of stars (red giants vs blue dwarfs) and the separation of solar (shortwave) from terrestrial (longwave) radiation that anchors the planetary energy balance.