Nox

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.