Parameterization of N2O5 reaction probabilities on the surface of particles containing ammonium, sulfate, and nitrate

A parameterization was developed for the heterogeneous reaction probability (gamma) of N2O5 as a function of temperature, relative humidity (RH), particle composition, and phase state. for use in advanced air quality models. The reaction probabilities on aqueous NH4HSO4, (NH4)(2)SO4, 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)(2)SO4 particles, yielding lower gamma values than the corresponding aqueous parameterizations. The regression equations reproduced 80% of the laboratory data within a factor of two and 63% within a factor of 1.5. A fixed value was selected for gamma 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, RH, sulfate, nitrate. and ammonium. The resulting spatial distributions of gamma were contrasted with three other parameterizations that have been applied in air quality models in the past and with atmospheric observational determinations of gamma. Our equations lay the foundation for future research that will parameterize the suppression of gamma when Inorganic ammoniated particles are mixed or coated with organic material. Our analyses draw attention to a major uncertainty in the available laboratory data at high RH and highlight a critical need for future laboratory ratory measurements of gamma at low temperature and high RH to improve model simulations of N2O5 hydrolysis during wintertime conditions.