Sensitivity of particulate matter nitrate formation to precursor emissionsin the California San Joaquin Valley

The formation of secondary ammonium nitrate during the 1995 Integrated Moni toring Study (IMS95) in San Joaquin Valley, CA was investigated using a box model that simulates the atmospheric chemistry and gas/particle partition of inorganic compounds. The concentration of particulate matter (PM) nitrat e was found to be sensitive to reductions in VOC emissions. Nitric acid, ra ther than ammonia, was the limiting reagent in the formation of PM nitrate. The formation of nitric acid was more sensitive to the availability of oxi dants than that of NOx. Oxidant chemistry in wintertime conditions in the S an Joaquin Valley was shown to be VOC-sensitive. In fact, a decrease in NOx emissions may have the counter-intuitive effect of increasing PM nitrate.