Global simulation of tropospheric O3‐NOx‐hydrocarbon chemistry: 1. Model formulation

We describe a global three‐dimensional model for tropospheric O 3 ‐NO x ‐hydrocarbon chemistry with synoptic‐scale resolution. A suite of 15 chemical tracers, including O 3 , NO x , PAN, HNO 3 , CO, H 2 O 2 , and various hydrocarbons, is simulated in the model. For computational expediency, chemical production and loss of tracers are parameterized as polynomial functions to fit the results of a detailed O 3 ‐NO x ‐hydrocarbon mechanism. The model includes state‐of‐the‐art inventories of anthropogenic emissions and process‐based formulations of natural emissions and deposition that are tied to the model meteorology. Improvements are made to existing schemes for computing biogenic emissions of isoprene and NO. Our best estimates of global emissions include among others 42 Tg N yr −1 for NO x (21 Tg N yr −1 from fossil fuel combustion, 12 Tg N yr −1 from biomass burning, 6 Tg N yr −1 from soils, and 3 Tg N yr −1 from lightning), and 37 Tg C yr −1 for acetone (1 Tg C yr −1 from industry, 9 Tg C yr −1 from biomass burning, 15 Tg C yr −1 from vegetation, and 12 Tg C yr −1 from oxidation of propane and higher alkanes).