The Treasure Valley secondary aerosol study II: modeling of the formation of inorganic secondary aerosols and precursors for southwestern Idaho

Many locations with very high mixing ratios of ammonia, nitrogen oxides and relatively low sulfate mixing ratios are found in urban areas of the western United States during the wintertime. These urban areas may also experience episodes with high humidity with high levels of secondary inorganic ammonium nitrate particles. Photochemical simulations of the formation of secondary sulfate and ammonium nitrate aerosol were made to investigate possible secondary particle control strategies for Treasure Valley, Idaho. The simulation conditions were based on the field study of Kuhns et al. (Atmos. Environ. 2002, this issue). It was found that under these conditions that almost all of the sulfate and approximately 95% of the nitric acid would be found in the particulate phase. Reductions in the emission rates of volatile organic compounds were found to be most effective in reducing secondary inorganic aerosol concentrations while reductions in nitrogen oxide emission rates would be expected to increase aerosol concentrations. This response of aerosol formation rates is due to the effects of the nitrogen oxide and volatile organic compound emission rates on the concentration of hydroxyl radical mixing ratios.