Parameterization of N2O5 reaction probabilities on the surface of particles containing ammonium, sulfate, and nitrate
1Atmospheric Modeling Division, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA
2Atmospheric Sciences Modeling Division, Air Resources Laboratory, National Oceanic and Atmospheric Administration, Research Triangle Park, NC, USA
*now at: North Carolina State University, Department of Marine, Earth, and Atmospheric Sciences, Raleigh, NC, USA
Abstract. A comprehensive parameterization was developed for the heterogeneous reaction probability (γ) of N2O5 as a function of temperature, relative humidity, particle composition, and phase state, for use in advanced air quality models. The reaction probabilities on aqueous NH4HSO4, (NH4)2SO4, and NH4NO3 were modeled statistically using data and uncertainty values compiled from seven different laboratory studies. A separate regression model was fit to laboratory data for dry NH4HSO4 and (NH4)2SO4 particles, yielding lower γ values than the corresponding aqueous parameterizations. The regression equations reproduced 79% of the laboratory data within a factor of two and 53% within a factor of 1.25. A fixed value was selected for γ on ice-containing particles based on a review of the literature. The combined parameterization was applied under atmospheric conditions representative of the eastern United States using 3-dimensional fields of temperature, relative humidity, sulfate, nitrate, and ammonium, obtained from a recent Community Multiscale Air Quality model simulation. The resulting spatial distributions of γ were contrasted with three other parameterizations that have been applied in air quality models in the past and with atmospheric observational determinations of γ. Our results highlight a critical need for more laboratory measurements of γ at low temperature and high relative humidity to improve model simulations of N2O5 hydrolysis during wintertime conditions.