RECEPTOR MODEL AND EMISSIONS INVENTORY SOURCE APPORTIONMENTS OF NONMETHANE ORGANIC GASES IN CALIFORNIA SAN-JOAQUIN VALLEY AND SAN-FRANCISCOBAY AREA

The chemical mass balance (CMB) receptor model was applied to the nonm ethane organic gas (NMOG) database acquired during the San Joaquin Val ley Air Quality Study (SJVAQS)/Atmospheric Utility Signatures-Predicti ons and Experiment (AUSPEX) Regional Model Adaptation Project (SARMAP) . During SARMAP, the major contributors to NMOG were vehicle exhaust, liquid gasoline, gasoline vapor, oil production, acetone and unidentif ied organic compounds. Oil production was the major contributor to NMO G in the southern SJV during the morning hours, ranging from about one -third to one-half of the total NMOG. Contributions of oil production were lower during the afternoon due to increased ventilation, and larg er contributions from secondary organic compounds. In the afternoon, t he combined fraction of acetone and unidentified or unexplained (diffe rence between calculated and measured mass) NMOG, which is mostly of s econdary origin, accounted for about half of the total NMOG at recepto r sites. Only the Yosemite and Giant Forest sites showed significant c ontributions from biogenic emissions. The fact that CMB did not detect significant contributions from biogenic sources in samples collected from sites in the SJV where estimated biogenic emission rates exceed t hose of either Yosemite or Giant Forest, suggests that biogenic emissi ons are overestimated in the SARMAP inventory. Source contribution est imates for total motor vehicle emissions averaged 75 and 70% of the to tal measured NMOG in urban areas during the 0800-1000 and 1200-1400 sa mpling periods, respectively, compared to the average daily emission i nventory contribution of 44%. These-results support recent studies whi ch indicate that motor vehicle emissions have been seriously underesti mated.