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 that surrounds Los Angeles experienced the worst photochemical smog episode in recent years; ozone concentrations exceeded 0.29 ppm 1-h average, and NO_2 concentrations peaked at 0.21 ppm 1-h average. Field measurements were conducted at a five-station air monitoring network to obtain comprehensive data on the identity and concentration of the individual organic compounds present in both the gas and particle phases during that episode. The data will also serve to support future tests of air quality models designed to study organic air pollutant transport and reaction. Air samples taken in stainless steel canisters were analyzed for 141 volatile organic compounds by GC/ECD, GC/FID, and GC/MS; PAN and PPN were measured by GC/ECD; particulate organics collected by filtration were analyzed for total organics and elemental carbon by thermal evolution and combustion and for individual organic compounds by GC/MS; semivolatile organics were analyzed by GC/MS after collection on polyurethane foam cartridges. The present paper describes this experiment and presents the concentrations of major organic compound classes and their relationship to the inorganic pollutants present. At the farthest downwind site studied (Claremont), extensive modification of primary 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 were 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), one fourth of the pollutant-derived nitrogen was in the particle phase, and nearly all of the Cl- had been removed from the particle phase. Of the total nitrate measured at Claremont, on the average only 33.6% was present as organic nitrates, which is a much lower ratio of organic nitrate to total nitrate than has been seen in previous years