Influence of modelled soil biogenic NO emissions on related trace gases and the atmospheric oxidizing efficiency

The emission of nitric oxide (NO) by soils (SNOx) is an important source of oxides of nitrogen (NO x =NO+NO 2) in the troposphere, with estimates ranging from 4 to 21 Tg of nitrogen per year. Previous studies have examined the influence of SNOx on ozone (O 3) chemistry. We employ the ECHAM5/MESSy earth system model to go further in 5 the reaction chain and investigate the influence of SNOx on lower tropospheric NO x , O 3 , peroxyaceltyl nitrate (PAN), nitric acid (HNO 3), the hydroxyl radical (OH) and the lifetime of methane (τ CH 4). We show that SNOx is responsible for a significant contribution to the NO x mixing ratio in many regions, especially in the tropics. On the other hand in some regions SNOx has a negative feedback on the lifetime of NO x through 10 O 3 and OH, which results in regional increases in the mixing ratio of NO x despite lower total emissions in a simulation without SNOx. Furthermore, the concentration of OH is substantially increased due to SNOx, resulting in an enhanced oxidizing efficiency of the global troposphere, reflected in a ∼10% decrease in τ CH 4 due to soil NO emissions.