The ammonium nitrate particle equivalent of NOx emissions for wintertime conditions in Central California's San Joaquin Valley

A new method has been developed to assess the aerosol particle formation re activity of nitrogen oxide (NOx) emissions. The method involves using a pho tochemical box model with gas-phase photochemistry, aerosol production and deposition to calculate the ammonium nitrate particle equivalent of NOx emi ssions. The yields of ammonium nitrate particles used in the box model were determined from parametric simulations made with an equilibrium model that calculated the fraction of nitric acid that reacts to produce ammonium nit rate from the temperature, relative humidity and ammonium-to-nitrate ratios . For the wintertime conditions of emissions and meteorology in the San Joa quin Valley of central California, approximately 80% of the moles of nitric acid produced was found to be in the particulate nitrate phase and about 3 3% of the moles of emitted NOx was converted to particulate nitrate. The pa rticle equivalent of NOx emissions was found to be on the order of 0.6 g of ammonium nitrate for each gram of NOx emitted (the mass of NOx calculated as NO2). This estimate is in reasonable agreement with an analysis of field measurements made in central California. (C) 2000 Elsevier Science Ltd. Al l rights reserved.