rate_DMSOH

{
  "reference": {
    "notes": "source_ref: GasChem.jl@8c12c048482b515fb8eb2110bf8ab4b4f4e71309:src/geoschem_ratelaws.jl:758 (`rate_DMSOH` rate-law builder function).\n\nRate law for DMS + OH -> 0.75SO2 + 0.25MSA + MO2 (addition channel): k = (k0*[M]*c2) / (1 + k1*c2) * C, where c2 = 0.2095 is the O2 mole fraction and k0, k1 are arrhenius_mlc_SI rates.\n\nMigration shape: the upstream `rate_DMSOH` returns a Catalyst `ReactionSystem` carrying zero reactions and one variable k(t) bound by a single algebraic equation k ~ <rate expression> (the @constants in the source are MTK unit-bookkeeping; their numeric values N_A=6.02214076e23, cm3_m3=1.0e6, ppb_unit=1.0e-9, k_unit_inv=1.0e6 are folded into the .esm expression AST as literals). It is migrated here as a purely-algebraic `model`: the rate-law inputs (T, num_density, Arrhenius coefficients) are `type: parameter`, the output k is the single `type: state` variable, and `equations` holds the one defining equation. No equation carries a D(.) operator, so the trajectory is constant in time and the inline test samples at t=0 (the observed-only convention of sibling files multiple_removal.esm / ope.esm).\n\nUnits: variables carry no `units` field — the rate expression folds the upstream MTK unit conversions into numeric literals, so every quantity is nominally dimensionless to the structural validator. This is the convention of the sibling GEOS-Chem file geoschem_fullchem.esm; physical units are documented in prose in each variable's `description`.\n\nTolerance rationale (model-level rel=1e-8 / abs=1e-30): the rate law is a single closed-form algebraic expression evaluated once (no time integration, no stiff dynamics). rel=1e-8 sits at the upstream Julia approximate-equality default (`approx` uses rtol=sqrt(eps(Float64))=~1.49e-8) and comfortably absorbs the libm exp / ^ / log10 rounding differences between the Julia reference values and the Python ESS runner; abs=1e-30 is a near-zero floor that gates no assertion here (the smallest pinned rate constant across the file is eq_const k=~2.1e-27).\n\nUpstream test reproduction: the inline test `upstream_rate_DMSOH` pins k at the parameter defaults to the value asserted by the `@testitem \"rate_DMSOH\"` block in GasChem.jl test/geoschem_ratelaws_test.jl, which compiles the rate law at T=293.0 K and num_density=2.7e19/N_A*cm3_m3 mol/m^3 and checks the resulting rate constant k."
  },
  "tolerance": {
    "rel": 1e-08,
    "abs": 1e-30
  },
  "variables": {
    "T": {
      "type": "parameter",
      "default": 293.0,
      "description": "Air temperature (K). Default 293.0 K is the scenario temperature of the upstream geoschem_ratelaws_test.jl `RateLawSetup` test snippet."
    },
    "num_density": {
      "type": "parameter",
      "default": 44.834554813693856,
      "description": "Number density of air (mol/m^3). Default 44.834554813693856 mol/m^3 equals 2.7e19 molec/cm^3 — the upstream test value 2.7e19/N_A*cm3_m3 (N_A = 6.02214076e23, cm3_m3 = 1.0e6)."
    },
    "a0": {
      "type": "parameter",
      "default": 1.12e-11,
      "description": "arrhenius_mlc_SI pre-exponential of k0."
    },
    "c0": {
      "type": "parameter",
      "default": -250.0,
      "description": "arrhenius_mlc_SI temperature term of k0. [K]"
    },
    "a1": {
      "type": "parameter",
      "default": 3e-31,
      "description": "arrhenius_mlc_SI pre-exponential of k1."
    },
    "c1": {
      "type": "parameter",
      "default": 4020.0,
      "description": "arrhenius_mlc_SI temperature term of k1. [K]"
    },
    "k": {
      "type": "unknown",
      "description": "Reaction rate coefficient produced by the rate_DMSOH rate law, output in ppb^-1*s^-1. Defined by one algebraic equation; the system carries no time derivative."
    }
  },
  "equations": [
    {
      "lhs": "k",
      "rhs": {
        "op": "*",
        "args": [
          {
            "op": "/",
            "args": [
              {
                "op": "*",
                "args": [
                  {
                    "op": "*",
                    "args": [
                      "a0",
                      {
                        "op": "*",
                        "args": [
                          {
                            "op": "exp",
                            "args": [
                              {
                                "op": "/",
                                "args": [
                                  "c0",
                                  "T"
                                ]
                              }
                            ]
                          },
                          {
                            "op": "^",
                            "args": [
                              {
                                "op": "/",
                                "args": [
                                  300.0,
                                  "T"
                                ]
                              },
                              0.0
                            ]
                          }
                        ]
                      },
                      1e-06
                    ]
                  },
                  1000000.0,
                  "num_density",
                  6.02214076e+17,
                  0.2095
                ]
              },
              {
                "op": "+",
                "args": [
                  1.0,
                  {
                    "op": "*",
                    "args": [
                      {
                        "op": "*",
                        "args": [
                          "a1",
                          {
                            "op": "*",
                            "args": [
                              {
                                "op": "exp",
                                "args": [
                                  {
                                    "op": "/",
                                    "args": [
                                      "c1",
                                      "T"
                                    ]
                                  }
                                ]
                              },
                              {
                                "op": "^",
                                "args": [
                                  {
                                    "op": "/",
                                    "args": [
                                      300.0,
                                      "T"
                                    ]
                                  },
                                  0.0
                                ]
                              }
                            ]
                          },
                          1e-06
                        ]
                      },
                      1000000.0,
                      0.2095
                    ]
                  }
                ]
              }
            ]
          },
          {
            "op": "*",
            "args": [
              "num_density",
              1e-09,
              6.02214076e+17
            ]
          }
        ]
      }
    }
  ],
  "tests": [
    {
      "id": "upstream_rate_DMSOH",
      "description": "Reproduces the upstream `rate_DMSOH` rate-law test (GasChem.jl test/geoschem_ratelaws_test.jl). All parameters are at their declared defaults — the exact coefficient values the upstream @testitem passes to `rate_DMSOH` — and the rate coefficient k is pinned to the upstream expected value 7.287375473764786e+17.",
      "parameter_overrides": {},
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "assertions": [
        {
          "variable": "k",
          "time": 0.0,
          "expected": 7.287375473764786e+17
        }
      ]
    }
  ]
}