We investigate the impact of new laboratory studies of N₂O₅ hydrolysis in aerosols on global model simulations of tropospheric chemistry. The new studies investigate the reactive uptake of N₂O₅ on a variety of tropospheric appropriate aerosol types (neutralized sulfate and organics) and under tropospheric appropriate temperatures and water vapor levels. We use data from these new studies together with recommendations from the literature to parameterize the reaction probability (γN₂O₅) in the GEOS-CHEM global model as a function of local aerosol composition, temperature, and relative humidity. We find a much lower global mean γN₂O₅ (0.02) than commonly assumed in models (0.1). Relative to a model simulation assuming a uniform γN₂O₅ = 0.1, we find increases in mass-averaged tropospheric NO_x, O₃, and OH concentrations of 7%, 4%, and 8% respectively. The increases in NO_x and O₃ concentrations bring the GEOS-CHEM simulation in better agreement with climatological observations of ozone from Logan [1998] and NO_x from Emmons et al. [2000]. A full description is given in Evans and Jacob, 2005.

Figure: Calculated zonal mean concentration ratios of OH, O₃ and NO_x for GEOS-CHEM model simulations with γN₂O₅ values calculated from the new laboratory studies versus a uniform value of 0.1. Results are seasonal averages for winter (DJF) and summer (JJA). Values greater than 1 indicate higher concentrations with the γN₂O₅ values calculated from new laboratory studies than with a uniform γN₂O₅ of 0.1. The lower values of γN₂O₅ found from the new laboratory studies results in higher NO_x concentrations. This then increases O₃ and OH concentrations due to higher formation rates of O₃ and recycling rates of HO₂ to OH. The impacts are largest in the relatively warm and dry downwards branches of the Hadley circulation.