AIR-QUALITY MODEL EVALUATION DATA FOR ORGANICS .1. BULK CHEMICAL-COMPOSITION AND GAS PARTICLE DISTRIBUTION FACTORS/

During the period of September 8-9, 1993, the South Coast Air Basin th at surrounds Los Angeles experienced the worst photochemical smog epis ode in recent years; ozone concentrations exceeded 0.29 ppm 1-h averag e, and NO2 concentrations peaked at 0.21 ppm 1-h average. Field measur ements were conducted at a five-station air monitoring network to obta in comprehensive data on the identity and concentration of the individ ual organic compounds present in both the gas and particle phases duri ng that episode. The data will also serve to support future tests of a ir quality models designed to study organic air pollutant transport an d reaction. Air samples taken in stainless steel canisters were analyz ed for 141 volatile organic compounds by GC/ECD, GC/FID, and GC/MS; PA N and PPN were measured by GC/ECD; particulate organics collected by f iltration were analyzed for total organics and elemental carbon by the rmal evolution and combustion and for individual organic compounds by GC/MS; semivolatile organics were analyzed by GC/MS after collection o n polyurethane foam cartridges. The present paper describes this exper iment and presents the concentrations of major organic compound classe s and their relationship to the inorganic pollutants present. At the f arthest downwind site studied (Claremont), extensive modification of p rimary pollutants by atmospheric chemical reactions was evident during the peak photochemical smog period: vapor-phase olefins and aromatics were depleted, the majority of the nitrogen-containing pollutants wer e present as organic plus inorganic nitrates, the fraction of organics in the particle phase rose to 12.5% (versus 2.6-5.4% at the coast), o ne fourth of the pollutant-derived nitrogen was in the particle phase, and nearly all of the Cl- had been removed from the particle phase. O f the total nitrate measured at Claremont, on the average only 33.6% w as present as organic nitrates, which is a much lower ratio of organic nitrate to total nitrate than has been seen in previous years.