Chemistry of the Earth's gas envelope: photochemistry of ozone, NOx/HOx/VOC cycles driving tropospheric oxidation, stratospheric halogen chemistry, aerosol formation, greenhouse-gas balance. Substrate of climate and air-quality modelling.
atmospheric-chemistry
Chapman mechanism (stratospheric ozone)
Four-reaction cycle forming/destroying stratospheric ozone: O₂+hν→2O (λ<242 nm), O+O₂+M→O₃, O₃+hν→O₂+O, O+O₃→2O₂. Predicts qualitative…
Catalytic ozone destruction (Cl, NO, HO_x)
X + O₃ → XO + O₂; XO + O → X + O₂ (net: O₃ + O → 2 O₂); each X atom destroys ~10⁴–10⁵ O₃ before removal. Active X: Cl (CFC source,…
Tropospheric HO_x chemistry
Hydroxyl radical OH, the 'detergent of the atmosphere', initiates oxidation of almost every VOC and CO. Principal source: O(¹D)+H₂O→2OH.…
Photochemical smog (NO_x + VOC)
Sunlight-driven oxidation of VOCs in NO_x-rich air yields ozone and PAN: RO₂ + NO → RO + NO₂; NO₂ + hν → NO + O; O + O₂ + M → O₃. PM₂.₅ and…
Atmospheric aerosol formation
Nucleation of H₂SO₄–H₂O–NH₃–organic clusters produces ultrafine particles (<3 nm) that grow by condensation and coagulation into CCN.…
Polar-vortex heterogeneous chemistry
On polar-stratospheric-cloud surfaces at <~195 K: HCl + ClONO₂ → Cl₂ + HNO₃. Spring sunlight photolyses Cl₂, launching catalytic O₃…
Greenhouse-gas radiative forcing
Molecules with ro-vibrational IR transitions in the 8–14 μm window (CO₂, CH₄, N₂O, H₂O, CFCs) absorb outgoing thermal radiation. Forcing ΔF…
Atmospheric photolysis (J-values)
First-order photolysis rate J = ∫σ(λ)ϕ(λ)F(λ)dλ with absorption cross-section σ, quantum yield ϕ, actinic flux F. Principal driver of…
Heterogeneous atmospheric chemistry
Solomon 1986 polar-stratospheric-cloud (PSC) reactions activate Cl from reservoirs HCl + ClONO₂ → Cl₂(g) + HNO₃(s) on ice-surface. …
Dimethyl sulfide & cloud-condensation (CLAW hypothesis)
Charlson-Lovelock-Andreae-Warren 1987: marine-phytoplankton produce DMS → atmospheric oxidation → SO₂ → sulfate-aerosol → CCN →…
Global atmospheric modelling (CMIP)
CMIP6 (Coupled Model Intercomparison Project, 2014-): standardised RCP/SSP scenarios across ~50 climate-models. General Circulation Models…
Methane radical oxidation (CH₄ lifetime)
Atmospheric CH₄ lifetime ~9 yr governed by reaction with OH radical: CH₄ + OH → CH₃ + H₂O (rate constant 6.3×10⁻¹⁵ cm³/s at 298 K). …
Atmospheric OH radical (atmospheric detergent)
Levy 1971: OH radical produced by O(1D) + H2O; primary oxidant of trace gases (CH4 / CO / VOCs); lifetime ~1 sec; abundance ~10^6 cm^-3 in…
NOx + tropospheric ozone production
Crutzen 1971 / Chameides-Walker 1973: NOx photolysis NO2 + hv -> NO + O; O + O2 -> O3; HOx-NOx coupling controls tropospheric ozone;…
Secondary organic aerosol (SOA)
VOC oxidation -> low-volatility products that condense onto particles; isoprene + monoterpenes biggest precursors; Hallquist 2009 review;…
Photolysis (actinic flux)
Atmospheric photolysis-rate j_X = integral sigma(lambda) phi(lambda) F(lambda) dlambda; F = actinic flux includes direct + scattered +…
Isotope fractionation (O17 mass-independent)
Thiemens-Heidenreich 1983 mass-independent fractionation in stratospheric O3 + via SO2-photolysis; Delta17O signal traces atmospheric O3…
DMS-cloud CLAW hypothesis
Charlson-Lovelock-Andreae-Warren 1987 CLAW: ocean DMS emissions oxidize to sulfate aerosol -> cloud-condensation nuclei -> increased…
O2 (Priestley 1774)
J Priestley 1774 + Lavoisier 1777 O2 isolation + role in combustion; foundation of atmospheric-gas chemistry.
NOx chain (Crutzen 1970)
P Crutzen 1970 (Nobel 1995) NOx-stratospheric-O3-cycle; modern N2O-radical + supersonic-aircraft + agricultural-N flux.
CFC-O3 (Rowland-Molina 1974)
S Rowland-M Molina 1974 (Nobel 1995) CFC-Cl-radical-O3-destruction; modern Montreal-Protocol 1987 + 2026 ozone-recovery.
Kerogen (Berner 1999)
R Berner 1999 GEOCARB + GEOCARBSULF; modern Phanerozoic CO2 / O2 reconstruction; modern volcanic-degassing constrained.
Köhler (1936)
H Köhler 1936 cloud-droplet-activation curvature-vs-solute Raoult; modern CCN-counter + indirect-aerosol-radiative-forcing.
Methane budget (Saunois 2020)
M Saunois 2020 GMP global-methane-budget; modern wetland + ag + fossil + isotope-13CH4 source-attribution constraint.