On the NO2 plus soot reaction in the atmosphere

Recent modeling studies have suggested that soot is a key component of trop ospheric chemistry in remote regions, acting to reduce HNO3 to NO2 and poss ibly NO2 to NO. It may be expected then that soot also affects the chemistr y of rural and urban areas, where soot concentrations are typically several orders of magnitude higher than in the remote, troposphere. In order to te st this assumption, a modeling study was conducted for typical urban and ru ral areas, with the same HNO3/NO2/soot chemistry proposed in the previous m odeling studies of the remote troposphere. Unreasonable results were found (e.g., nearly total suppression of urban ozone, in contradiction to common observations), suggesting that the NO2/soot reaction was considerably overe stimated in previous modeling studies. Therefore the NO2/soot chemistry was reconsidered. A new preliminary mechanism is suggested, based on recent la boratory studies of this reaction. Results show that the NO2/soot reaction does not notably affect the Ox-NOx-HOx chemistry of the lower continental t roposphere, except maybe during nighttime in urban environments. A potentia l contribution of the NO2/soot interaction to HONO production is noted.