SPATIAL AND TEMPORAL VARIATIONS OF PARTICULATE PRECURSOR GASES AND PHOTOCHEMICAL-REACTION PRODUCTS DURING SJVAQS AUSPEX OZONE EPISODES/

SJVAQS/AUSPEX acquired PM2.5, PM10, and gas samples at ten sites in ce ntral California during five ozone episodes over a period of 14 intens ive sampling days. Four sample sets per day were collected for 5- and 7-hour durations during this period and analyzed for particulate mass, elements, ions, and organic and elemental carbon (OC and EC). Gaseous ammonia, nitric acid, and sulfur dioxide were collected with absorbin g filters. Ozone (O-3), nitrogen oxides (NOx), and peroxyacetyl nitrat e (PAN) were measured continuously. Concentrations varied by sampling site, time of the day, and ozone episode. The highest concentrations o f most chemical species were found at sites in the southern San Joaqui n Valley. Nitrate occurred mainly in the gas phase during the daytime when temperatures exceeded 25 degrees C, and in the particulate phase during the nighttime when temperatures decreased to less than 10 degre es C. Significant amounts of nitrate volatilized from particles collec ted on quartz-fiber filters. Diurnal patterns of ozone, nitrogen oxide s, PAN, nitric acid, and total particle citrate were similar at most o f the sites, which were separated by hundreds of kilometers, showing e vidence of both photochemical conversion and transport of polluted air masses. (C) 1998 Elsevier Science Ltd. All rights reserved.