Quantification of the factors controlling tropical tropospheric ozone and the South Atlantic maximum

[1] We quantify the processes controlling the tropical tropospheric ozone burden with particular attention to the tropical Atlantic, using a global chemical transport model (GEOS-Chem) constrained by satellite and in situ observations of O-3, NO2, and HCHO. Lightning is the dominant contributor to tropical tropospheric O-3, accounting for more than 37% of the O-3 burden over the Atlantic on annual average. The contributions from biomass burning, soils, and fossil fuels are 4 to 6 times smaller, despite comparable source strengths. This discrepancy can be explained by the tropical ozone production efficiency of lightning ( 32 mol/ mol), soils ( 14 mol/ mol), biomass burning ( 10 mol/ mol), and fossil fuel ( 13 mol/ mol) sources, as calculated using sensitivity simulations with a 1% perturbation. The role of volatile organic compound emissions on the tropical Atlantic ozone burden is negligible (< 2.5%). Stratosphere-troposphere exchange accounts for less than 5% of the regional O-3 burden. The tropical Atlantic O-3 burden is more strongly influenced by nitrogen oxides from Africa (> 30%) than from South America (> 18%) or the eastern tropics (> 11%). Lightning is responsible for more than 39% of the atmospheric oxidation capacity, higher than other sources. The dominant sources of uncertainty in the tropical oxidation rate are the lightning magnitude and the cloud convective parameterization.