OHReactionLifetime

{
  "reference": {
    "notes": "source_ref: GasChem.jl@280ee50fbc8fb6d8bdf4b12c9ef1c506fe890551:src/AtmosphericLifetime.jl:264\n\nUpstream `OHReactionLifetime` is an MTK `@component` declaring one `@parameter` (k_OH, the second-order OH reaction rate constant), three time-indexed `@variables` (OH_conc the input OH number density; k_eff and tau_OH the two outputs), zero `@constants`, and two algebraic equations. It implements Seinfeld & Pandis (2006) Ch. 2 Eq. 2.12 — the atmospheric lifetime of a trace species against removal by reaction with the hydroxyl radical, tau = 1 / (k_OH*[OH]). OH is the dominant daytime tropospheric oxidant, so this lifetime sets the persistence of most reactive trace gases (CH4, CO, non-methane VOCs). The upstream docstring notes the product k_OH*[OH] is an effective first-order rate constant 'consistent with Eq. 2.6'.\n\nVariable-classification convention: the input @variable OH_conc is encoded here as `type: parameter` because it has no defining equation within the OHReactionLifetime component itself — it is an externally-supplied ambient OH concentration. The upstream structural test `1.4 OHReactionLifetime Structure` (test/atmospheric_lifetime_test.jl) builds the raw `@named` System where OH_conc is still an `unknown`; the canonical simulate path compiles such an input-bearing component with `mtkcompile(sys; inputs=[OH_conc])`, which resolves the input @variable into a parameter. This mirrors the rig-wide convention applied by sibling oh_production.esm (input @variables O3/H2O/M encoded as `type: parameter`), ope.esm (OH/HO2/RO2/NO/NO2), and the same-source-file sibling tropospheric_budget.esm (P_n/P_a/P_c). The single declared @parameter k_OH carries `type: parameter` directly. The two output @variables k_eff and tau_OH are encoded as `type: state` — each is the LHS of exactly one algebraic equation; this matches the sibling observed-only gaschem ESM convention (ope.esm P_O3/L_NOx/OPE all `type: state`, oh_production.esm O1D/P_OH/eps_OH all `type: state`).\n\nStructural-test reproduction: upstream `1.4 OHReactionLifetime Structure` asserts the raw System carries the three variable names OH_conc/k_eff/tau_OH among `unknowns`, k_OH among `parameters`, and `length(equations) == 2`. The .esm preserves this with four declared variables (2 parameter k_OH+OH_conc, 2 state k_eff+tau_OH — together the four symbols that upstream splits into 3 unknowns + 1 parameter) and exactly two entries in `equations`.\n\nCGS->SI unit translation: the upstream Julia declares the component in CGS units — k_OH as u\"cm^3/(molec*s)\", OH_conc as u\"molec/cm^3\", k_eff as u\"s^-1\", tau_OH as u\"s\" — and carries no `default =` value on either k_OH or OH_conc. The .esm declares the two number-density-bearing quantities in SI, dropping the dimensionless `molec` count: k_OH in m^3/s and OH_conc in m^-3, matching the rig-wide SI unit vocabulary (no committed .esm uses `cm^3` or `molec`; siblings oh_production.esm and ope.esm convert the identical CGS rate-constant and number-density quantities to m^3/s and m^-3). The conversion is exact and physics-invariant for the two outputs: k_OH[m^3/s] = k_OH[cm^3/molec/s] * 1e-6 (1 cm^3 = 1e-6 m^3) and OH_conc[m^-3] = OH_conc[molec/cm^3] * 1e6 (1 cm^-3 = 1e6 m^-3), so their product k_eff = k_OH*OH_conc is unchanged (the *1e-6 and *1e6 factors cancel) and tau_OH = 1/k_eff is likewise unchanged. Both equations are unit-system-agnostic in form; only the input/parameter literals carry the conversion. Unlike sibling ope.esm — whose upstream Julia already wrote the rate constants as the SI-converted product (8.1e-12 * 1.0e-6) — the OHReactionLifetime upstream is purely CGS, so this migration introduces the conversion: the .esm encodes the clean SI literals (6.3e-21, 2.4e-19, 1.0e-16, 1.0e-20 m^3/s; 1.0e12 m^-3) directly.\n\nObservability classification: this component is purely algebraic — both equations are `~` assignment relations with no `D(.)` time-derivative operator, so the `(t)` time index has no dynamical role and every trajectory is constant in time. Test and example scenarios use time_span [0.0, 1.0] and sample at t=0, mirroring the convention of sibling observed-only ESM files (ope.esm, oh_production.esm, gwp.esm).\n\nEquation cascade: the two equations form a topologically-ordered cascade — k_eff depends only on the parameter k_OH and the input OH_conc; tau_OH depends on k_eff. tau_OH's equation is written `tau_OH ~ 1 / k_eff` (referencing the k_eff output) rather than fully inlined as 1/(k_OH*OH_conc) — this preserves the upstream symbolic structure, which splits the lifetime into an explicit pseudo-first-order rate constant k_eff and its reciprocal, mirroring the ope.esm `OPE ~ P_O3/L_NOx` and oh_production.esm cascade convention.\n\nNumerical defaults: the upstream input @variable OH_conc and @parameter k_OH carry no defaults — the .esm defaults are taken from the canonical upstream verification test `2.9 Eq. 2.12: OH Reaction Lifetime` (test/atmospheric_lifetime_test.jl), the methane scenario:\n  k_OH    = 6.3e-21 m^3/s   (methane + OH; upstream CGS 6.3e-15 cm^3/molec/s)\n  OH_conc = 1.0e12 m^-3     (global tropospheric mean OH; upstream CGS 1.0e6 molec/cm^3)\nAt these defaults k_eff = 6.3e-9 s^-1 and tau_OH = 158730158.73015872 s ~= 5.03 Julian years — the canonical methane OH-lifetime. Methane is the textbook illustration of an OH-controlled lifetime; the upstream docstring's stated 'tau: seconds to years' range is anchored at its long-lived end by exactly this CH4 case.\n\nUpstream test reproduction:\n- `1.4 OHReactionLifetime Structure` (test/atmospheric_lifetime_test.jl) — reproduced by the .esm structural shape (4 variables = 2 parameter + 2 state, 2 equations).\n- `2.9 Eq. 2.12: OH Reaction Lifetime` (test/atmospheric_lifetime_test.jl) — a pure-arithmetic verification of tau = 1/(k_OH*[OH]) for two species: methane (k_OH=6.3e-15 cm^3/molec/s, [OH]=1e6 molec/cm^3 -> tau ~= 5.0 years, upstream rtol=0.1) and carbon monoxide (k_OH=2.4e-13 cm^3/molec/s -> tau ~= 48 days, upstream rtol=0.1). Reproduced and tightened to rel=1e-10 by `upstream_eq212_methane_lifetime_defaults` (CH4, at the declared defaults) and `upstream_eq212_carbon_monoxide_lifetime` (CO, k_OH overridden to 2.4e-19 m^3/s). The CO pinned values are computed from the .esm's own SI literal 2.4e-19 m^3/s — k_eff = 2.4e-19*1.0e12 = 2.4000000000000003e-07 s^-1, tau_OH = 4166666.666666666 s — internally exact at rel=1e-10; this differs from the upstream CGS arithmetic 1/(2.4e-13*1e6) by one ULP (~2e-16 relative, six orders of magnitude below the upstream rtol=0.1).\nThe remaining eight tests extend coverage beyond the upstream suite: inverse scaling of tau_OH in OH_conc (doubled, halved), the k_OH<->OH_conc product symmetry (doubling k_OH gives a lifetime bit-identical to doubling OH_conc), the docstring's stated k_OH range endpoints (1e-14 and 1e-10 cm^3/molec/s — slowly- and highly-reactive species), the clean-remote and polluted-daytime OH regimes, and a joint two-input perturbation.\n\nTolerance rationale (model-level rel=1.0e-10 / abs=1.0e-12): the two algebraic equations are minimal expression trees — k_eff is a single two-factor product (1 IEEE-754 op), tau_OH a single reciprocal (1 op). Each output is correctly-rounded to within ~1 ULP ~= 1e-16 relative; rel=1e-10 leaves six orders of magnitude of headroom and is far tighter than the upstream test 2.9's rtol=0.1. No test scenario produces a zero or near-zero output (the smallest pinned magnitudes are k_eff ~= 1e-4 s^-1 and tau_OH = 1e4 s, in the highly-reactive case), so the abs=1.0e-12 floor is never the binding tolerance; it is retained as a model-level floor matching the sibling observed-only ESM convention (ope.esm rel=1e-10/abs=1e-12, oh_production.esm rel=1e-10/abs=1e-12). The OH_conc->0 boundary (k_eff->0, tau_OH = 1/0 -> +Inf) is deliberately not exercised as a test scenario — a non-finite expected value has no meaningful rel/abs tolerance — and no example sweep reaches OH_conc = 0.\n\nUnit balance (verified): both equations balance dimensionally.\n  k_eff  `k_OH*OH_conc`: (m^3/s)*(m^-3) = s^-1 ok\n  tau_OH `1 / k_eff`: 1/(s^-1) = s ok (the literal 1 is dimensionless)\nAll number densities in SI m^-3, the rate constant in SI m^3/s, the effective first-order rate constant in s^-1, the lifetime in s. SI throughout; no unit conversion at parse or runtime."
  },
  "tolerance": {
    "rel": 1e-10,
    "abs": 1e-12
  },
  "variables": {
    "k_OH": {
      "type": "parameter",
      "units": "m^3/s",
      "default": 6.3e-21,
      "description": "Second-order (bimolecular) rate constant for the trace-species + OH reaction [m^3/s] (Seinfeld & Pandis 2006 Ch. 2, Eq. 2.12). The intrinsic OH reactivity of the species, which with the ambient OH concentration sets the effective first-order loss rate k_eff = k_OH*OH_conc. The default 6.3e-21 m^3/s is the methane + OH rate constant — the SI form of the upstream CGS value 6.3e-15 cm^3/molec/s (1 cm^3 = 1e-6 m^3, the dimensionless `molec` count dropped). The upstream docstring quotes a typical species range of 1e-14 to 1e-10 cm^3/molec/s (1e-20 to 1e-16 m^3/s); methane, exceptionally unreactive, sits just below it. Encoded as `type: parameter`: it is the component's sole upstream @parameter, set via parameter_overrides in tests and parameter sweeps in examples."
    },
    "OH_conc": {
      "type": "parameter",
      "units": "m^-3",
      "default": 1000000000000.0,
      "description": "Ambient hydroxyl-radical number density [m^-3] (externally-supplied input). The default 1.0e12 m^-3 ~= 1e6 molec/cm^3 is the global tropospheric mean OH concentration and is the value used by the upstream verification test `2.9 Eq. 2.12` for both its methane and carbon-monoxide cases; it is the SI form of the upstream CGS 1.0e6 molec/cm^3 (1 cm^-3 = 1e6 m^-3). OH appears only in k_eff = k_OH*OH_conc, so the OH-reaction lifetime tau_OH is exactly inversely proportional to OH_conc — a higher ambient OH burden shortens the lifetime of every species. Encoded as `type: parameter` (not `type: state`) because OHReactionLifetime has no governing equation for OH_conc — it is an externally-supplied input variable, resolved into a parameter by the canonical mtkcompile(sys; inputs=[OH_conc]) compile path."
    },
    "k_eff": {
      "type": "unknown",
      "units": "s^-1",
      "description": "Effective pseudo-first-order rate constant for loss by OH reaction [s^-1]: k_eff = k_OH*OH_conc. Collapses the second-order reaction X + OH into a first-order decay constant for X by absorbing the (approximately constant) OH concentration — the standard pseudo-first-order treatment, consistent with Eq. 2.6 of Seinfeld & Pandis (2006). At the methane default scenario k_eff = 6.3e-9 s^-1. Exactly linear in both k_OH and OH_conc."
    },
    "tau_OH": {
      "type": "unknown",
      "units": "s",
      "description": "Atmospheric lifetime of the trace species against removal by reaction with OH [s] (Seinfeld & Pandis 2006 Ch. 2, Eq. 2.12): tau_OH = 1/k_eff = 1/(k_OH*[OH]). The e-folding time for first-order decay of the species under OH oxidation. At the methane default scenario tau_OH ~= 1.587e8 s ~= 5.03 years; carbon monoxide (~38x more reactive) is ~48 days. Inversely proportional to both the species reactivity k_OH and the ambient OH concentration — the OH-reaction lifetime spans seconds (fast alkenes in polluted air) to years (CH4 in clean air)."
    }
  },
  "equations": [
    {
      "lhs": "k_eff",
      "rhs": {
        "op": "*",
        "args": [
          "k_OH",
          "OH_conc"
        ]
      }
    },
    {
      "lhs": "tau_OH",
      "rhs": {
        "op": "/",
        "args": [
          1,
          "k_eff"
        ]
      }
    }
  ],
  "tests": [
    {
      "id": "upstream_eq212_methane_lifetime_defaults",
      "description": "Reproduces and tightens the methane branch of the upstream `2.9 Eq. 2.12: OH Reaction Lifetime` test (GasChem.jl test/atmospheric_lifetime_test.jl). At the declared defaults k_OH=6.3e-21 m^3/s (methane + OH, upstream CGS 6.3e-15 cm^3/molec/s) and OH_conc=1.0e12 m^-3 (global tropospheric mean OH, upstream CGS 1.0e6 molec/cm^3): k_eff = k_OH*OH_conc = 6.3e-9 s^-1 and tau_OH = 1/k_eff = 158730158.73015872 s = 5.0299 Julian years. The upstream asserts tau_CH4 in years ~= 5.0 at rtol=0.1; this test pins both outputs to single-ULP precision at rel=1e-10, nine orders of magnitude tighter. Because nothing is overridden it also guards the k_OH and OH_conc defaults: any drift in either shifts both pinned values.",
      "parameter_overrides": {},
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "assertions": [
        {
          "variable": "k_eff",
          "time": 0.0,
          "expected": 6.3e-09
        },
        {
          "variable": "tau_OH",
          "time": 0.0,
          "expected": 158730158.73015872
        }
      ]
    },
    {
      "id": "upstream_eq212_carbon_monoxide_lifetime",
      "description": "Reproduces and tightens the carbon-monoxide branch of the upstream `2.9 Eq. 2.12` test. k_OH overridden to 2.4e-19 m^3/s (CO + OH, upstream CGS 2.4e-13 cm^3/molec/s), OH_conc at the default 1.0e12 m^-3. k_eff = 2.4000000000000003e-07 s^-1, tau_OH = 4166666.666666666 s = 48.2253 days. The upstream asserts tau_CO in days ~= 48 at rtol=0.1; this test pins both outputs at rel=1e-10. The pinned values are computed from the .esm's own SI literal 2.4e-19; they differ from the upstream CGS arithmetic 1/(2.4e-13*1e6) by one ULP (~2e-16 relative), six orders of magnitude inside the upstream rtol=0.1. CO is ~38x more reactive toward OH than CH4, so its OH lifetime is ~38x shorter (weeks, not years).",
      "parameter_overrides": {
        "k_OH": 2.4e-19
      },
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "assertions": [
        {
          "variable": "k_eff",
          "time": 0.0,
          "expected": 2.4000000000000003e-07
        },
        {
          "variable": "tau_OH",
          "time": 0.0,
          "expected": 4166666.666666666
        }
      ]
    },
    {
      "id": "oh_conc_doubled_halves_lifetime",
      "description": "OH_conc doubled to 2.0e12 m^-3, k_OH at the CH4 default. k_eff = k_OH*OH_conc is exactly linear in OH_conc, so k_eff doubles to 1.26e-8 s^-1 and tau_OH = 1/k_eff halves to 79365079.36507936 s (2.515 yr). Verifies the inverse proportionality tau_OH ~ 1/[OH]: a more oxidising (higher-OH) atmosphere removes the trace species twice as fast.",
      "parameter_overrides": {
        "OH_conc": 2000000000000.0
      },
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "assertions": [
        {
          "variable": "k_eff",
          "time": 0.0,
          "expected": 1.26e-08
        },
        {
          "variable": "tau_OH",
          "time": 0.0,
          "expected": 79365079.36507936
        }
      ]
    },
    {
      "id": "oh_conc_halved_doubles_lifetime",
      "description": "OH_conc halved to 5.0e11 m^-3, k_OH at the CH4 default. k_eff halves to 3.15e-9 s^-1 and tau_OH doubles to 317460317.46031743 s (10.06 yr). The downward-OH counterpart of `oh_conc_doubled_halves_lifetime` — together they bracket the default scenario and confirm tau_OH is exactly inversely proportional to the ambient OH concentration.",
      "parameter_overrides": {
        "OH_conc": 500000000000.0
      },
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "assertions": [
        {
          "variable": "k_eff",
          "time": 0.0,
          "expected": 3.15e-09
        },
        {
          "variable": "tau_OH",
          "time": 0.0,
          "expected": 317460317.46031743
        }
      ]
    },
    {
      "id": "k_oh_doubled_matches_oh_doubled_symmetry",
      "description": "k_OH doubled to 1.26e-20 m^3/s, OH_conc at the default 1.0e12 m^-3. k_eff = k_OH*OH_conc depends only on the product, so k_eff = 1.26e-8 s^-1 and tau_OH = 79365079.36507936 s — bit-identical to the `oh_conc_doubled_halves_lifetime` result. Verifies the k_OH<->OH_conc product symmetry: doubling the intrinsic reactivity of the species is numerically indistinguishable from doubling the ambient OH. A regression that wired k_eff to only one of the two factors would break exactly one of this test / `oh_conc_doubled_halves_lifetime`.",
      "parameter_overrides": {
        "k_OH": 1.26e-20
      },
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "assertions": [
        {
          "variable": "k_eff",
          "time": 0.0,
          "expected": 1.26e-08
        },
        {
          "variable": "tau_OH",
          "time": 0.0,
          "expected": 79365079.36507936
        }
      ]
    },
    {
      "id": "highly_reactive_species_short_lifetime",
      "description": "Highly reactive trace species: k_OH = 1.0e-16 m^3/s, the upper end of the upstream docstring's stated k_OH range (1e-10 cm^3/molec/s). OH_conc at the default. k_eff = 9.999999999999999e-05 s^-1, tau_OH = 10000.0 s (2.78 hours) — the short-lived end of the docstring's 'seconds to years' span. Representative of fast-oxidising species (many alkenes, terpenes) that are destroyed within hours of emission.",
      "parameter_overrides": {
        "k_OH": 1e-16
      },
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "assertions": [
        {
          "variable": "k_eff",
          "time": 0.0,
          "expected": 9.999999999999999e-05
        },
        {
          "variable": "tau_OH",
          "time": 0.0,
          "expected": 10000.0
        }
      ]
    },
    {
      "id": "slowly_reactive_species_long_lifetime",
      "description": "Slowly reactive trace species: k_OH = 1.0e-20 m^3/s, the lower end of the upstream docstring's stated k_OH range (1e-14 cm^3/molec/s). OH_conc at the default. k_eff = 1e-08 s^-1, tau_OH = 100000000.0 s (3.169 yr). Confirms that an unreactive species accumulates a multi-year OH lifetime; methane (k_OH=6.3e-21, even less reactive) sits just below this bound at ~5 yr.",
      "parameter_overrides": {
        "k_OH": 1e-20
      },
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "assertions": [
        {
          "variable": "k_eff",
          "time": 0.0,
          "expected": 1e-08
        },
        {
          "variable": "tau_OH",
          "time": 0.0,
          "expected": 100000000.0
        }
      ]
    },
    {
      "id": "clean_remote_low_oh_long_lifetime",
      "description": "Clean remote atmosphere: OH_conc lowered to 1.0e11 m^-3 (~1e5 molec/cm^3, an order of magnitude below the global mean), k_OH at the CH4 default. k_eff = 6.3e-10 s^-1, tau_OH = 1587301587.3015873 s (50.30 yr). With little OH available the methane lifetime stretches tenfold — illustrating that the OH-reaction lifetime is set jointly by species reactivity and the ambient oxidant burden.",
      "parameter_overrides": {
        "OH_conc": 100000000000.0
      },
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "assertions": [
        {
          "variable": "k_eff",
          "time": 0.0,
          "expected": 6.3e-10
        },
        {
          "variable": "tau_OH",
          "time": 0.0,
          "expected": 1587301587.3015873
        }
      ]
    },
    {
      "id": "polluted_high_oh_short_lifetime",
      "description": "Polluted daytime atmosphere: OH_conc raised to 1.0e13 m^-3 (~1e7 molec/cm^3, a daytime urban-plume peak), k_OH at the CH4 default. k_eff = 6.3e-08 s^-1, tau_OH = 15873015.873015875 s (183.7 days = 0.503 yr). The high-OH counterpart of `clean_remote_low_oh_long_lifetime`: a tenfold rise in OH compresses the methane lifetime tenfold, from ~5 yr to ~6 months.",
      "parameter_overrides": {
        "OH_conc": 10000000000000.0
      },
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "assertions": [
        {
          "variable": "k_eff",
          "time": 0.0,
          "expected": 6.3e-08
        },
        {
          "variable": "tau_OH",
          "time": 0.0,
          "expected": 15873015.873015875
        }
      ]
    },
    {
      "id": "carbon_monoxide_in_polluted_air_joint_perturbation",
      "description": "Joint two-input perturbation: k_OH = 2.4e-19 m^3/s (CO) and OH_conc = 5.0e12 m^-3 (5x the mean, a moderately polluted air mass) both overridden away from the CH4 defaults. k_eff = 1.2000000000000002e-06 s^-1, tau_OH = 833333.3333333333 s (9.645 days). Exercises both equation inputs simultaneously to catch cross-wiring between the k_OH and OH_conc slots of k_eff; the result is the product of the CO reactivity and the elevated OH.",
      "parameter_overrides": {
        "k_OH": 2.4e-19,
        "OH_conc": 5000000000000.0
      },
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "assertions": [
        {
          "variable": "k_eff",
          "time": 0.0,
          "expected": 1.2000000000000002e-06
        },
        {
          "variable": "tau_OH",
          "time": 0.0,
          "expected": 833333.3333333333
        }
      ]
    }
  ],
  "analyses": [
    {
      "id": "lifetime_vs_oh_rate_constant_sweep",
      "description": "OH-reaction lifetime and effective rate constant as functions of the species rate constant k_OH, swept logarithmically from 1.0e-21 to 1.0e-16 m^3/s (upstream CGS 1e-15 to 1e-10 cm^3/molec/s) with OH_conc at the global-mean default 1.0e12 m^-3. The sweep spans the full reactivity range of tropospheric trace gases: methane (k_OH=6.3e-21) near the slow end, carbon monoxide (k_OH=2.4e-19) mid-range, and fast-oxidising alkenes/terpenes near 1e-16. Because tau_OH = 1/(k_OH*[OH]), the lifetime falls as 1/k_OH across five decades — from decades down to hours — the continuous form of the textbook species-lifetime table of Seinfeld & Pandis (2006) Ch. 2.",
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "parameter_sweep": {
        "type": "cartesian",
        "dimensions": [
          {
            "parameter": "k_OH",
            "range": {
              "start": 1e-21,
              "stop": 1e-16,
              "count": 60,
              "scale": "log"
            }
          }
        ]
      },
      "plots": [
        {
          "id": "tau_oh_vs_k_oh",
          "type": "line",
          "description": "OH-reaction lifetime tau_OH vs the species rate constant k_OH on log-log axes. A straight falling line of slope -1 (tau_OH proportional to 1/k_OH at fixed OH): the more reactive the species, the shorter its atmospheric persistence, dropping from ~32 yr at k_OH=1e-21 to ~3 hours at k_OH=1e-16.",
          "x": {
            "variable": "k_OH",
            "label": "OH rate constant k_OH (m^3/s, log)"
          },
          "y": {
            "variable": "tau_OH",
            "label": "OH-reaction lifetime tau_OH (s, log)"
          }
        },
        {
          "id": "k_eff_vs_k_oh",
          "type": "line",
          "description": "Effective pseudo-first-order rate constant k_eff = k_OH*OH_conc vs k_OH. A straight rising line through the origin (k_eff exactly linear in k_OH at fixed OH_conc) — the loss rate that drives the tau_OH decline.",
          "x": {
            "variable": "k_OH",
            "label": "OH rate constant k_OH (m^3/s, log)"
          },
          "y": {
            "variable": "k_eff",
            "label": "effective rate constant k_eff (s^-1, log)"
          }
        }
      ]
    },
    {
      "id": "lifetime_vs_oh_concentration_sweep",
      "description": "Methane OH-reaction lifetime as a function of the ambient OH concentration, swept logarithmically from 1.0e10 to 1.0e13 m^-3 (upstream CGS 1e4 to 1e7 molec/cm^3) with k_OH at the methane default 6.3e-21 m^3/s. The range runs from a clean remote free-troposphere OH burden up to a daytime polluted-plume peak. tau_OH = 1/(k_OH*[OH]) falls as 1/[OH], so the same molecule's lifetime varies by three orders of magnitude purely with the oxidising capacity of the surrounding air — the mechanism behind the seasonal and latitudinal spread of the methane lifetime.",
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "parameter_sweep": {
        "type": "cartesian",
        "dimensions": [
          {
            "parameter": "OH_conc",
            "range": {
              "start": 10000000000.0,
              "stop": 10000000000000.0,
              "count": 60,
              "scale": "log"
            }
          }
        ]
      },
      "plots": [
        {
          "id": "tau_oh_vs_oh_conc",
          "type": "line",
          "description": "Methane OH-reaction lifetime tau_OH vs ambient OH number density on log-log axes. A straight falling line of slope -1 (tau_OH proportional to 1/[OH]): higher OH shortens the lifetime from ~500 yr in the cleanest air to ~6 months at a polluted daytime OH peak.",
          "x": {
            "variable": "OH_conc",
            "label": "OH number density (m^-3, log)"
          },
          "y": {
            "variable": "tau_OH",
            "label": "OH-reaction lifetime tau_OH (s, log)"
          }
        }
      ]
    },
    {
      "id": "lifetime_heatmap_k_oh_oh_conc",
      "description": "OH-reaction lifetime as a joint function of species reactivity k_OH and ambient OH concentration (2-D log-log sweep). k_OH in [1.0e-21, 1.0e-16] m^3/s x OH_conc in [1.0e10, 1.0e13] m^-3. Because tau_OH = 1/(k_OH*[OH]) depends only on the product k_OH*[OH], the iso-lifetime contours are straight anti-diagonal lines of constant k_OH*OH_conc: the long-lived corner is the unreactive species in clean air (low k_OH, low OH), the short-lived corner is the reactive species in polluted air (high k_OH, high OH). Surfaces the full bivariate structure that the two 1-D sweeps each section.",
      "time_span": {
        "start": 0.0,
        "end": 1.0
      },
      "parameter_sweep": {
        "type": "cartesian",
        "dimensions": [
          {
            "parameter": "k_OH",
            "range": {
              "start": 1e-21,
              "stop": 1e-16,
              "count": 25,
              "scale": "log"
            }
          },
          {
            "parameter": "OH_conc",
            "range": {
              "start": 10000000000.0,
              "stop": 10000000000000.0,
              "count": 20,
              "scale": "log"
            }
          }
        ]
      },
      "plots": [
        {
          "id": "tau_oh_heatmap_k_oh_oh_conc",
          "type": "heatmap",
          "description": "tau_OH as a function of (k_OH, OH_conc) on log-log axes. The iso-lifetime contours run anti-diagonally as lines of constant k_OH*OH_conc product: the lower-left region (low reactivity, low OH) is the long-lived regime, the upper-right region (high reactivity, high OH) is the short-lived regime.",
          "x": {
            "variable": "k_OH",
            "label": "OH rate constant k_OH (m^3/s, log)"
          },
          "y": {
            "variable": "OH_conc",
            "label": "OH number density (m^-3, log)"
          },
          "value": {
            "variable": "tau_OH",
            "reduce": "final"
          }
        }
      ]
    }
  ]
}