The contribution of sulfate and nitrate to atmospheric fine particles during winter inversion fogs in Cache Valley, Utah

Air pollutants were collected in Logan, Cache County, UT, in February 1993 during two periods of atmospheric inversion accompanied by fog. The following atmospheric species were determined: (1) gaseous SO,, NO, (semi-quantitatively), HNO3, NH3, and HF; (2) fine particulate SO4, NO3,(-) NH4'+ F-, H+, C, Si, S, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Pb, Se, Br, and Sr; and (3) fine particulate mass, which was calculated. The major components of fine particulate matter were carbonaceous material, ammonium nitrate, and ammonium sulfate, while the soil component was small. Calculated, fine particulate mass averaged 80 mu g/m(3) and reached concentrations as high as 120 mu g/m(3). SO2/SOx and NO2/NOy mole ratios generally varied between 0.2 and 0.1 during inversions. These ratios also showed moderate but consistent diurnal patterns. The emission inventory for Cache County indicates sources of SO2 and NOx but not significant amounts of primary sulfate and nitrate. The observations reported here indicate there is significant conversion of SO2 and NOx in the presence of excess oxidants to sulfuric and nitric acid that are neutralized by excess ammonia.