AIR-QUALITY MODEL EVALUATION DATA FOR ORGANICS .2. C-1-C-14 CARBONYLSIN LOS-ANGELES AIR

As part of a larger experiment that provides a comprehensive set of ob servations to be used for testing air quality models for organic air p ollutant transport and reaction, ambient air samples have been collect ed using DNPH-coated C-18 cartridges at four urban locations and one b ackground location in the Los Angeles area and have been analyzed for carbonyls as their DNPH derivatives. Twenty-three carbonyls have been identified and their concentrations measured: 14 aliphatic aldehydes ( from formaldehyde to tetradecanal), two aromatics (benzaldehyde and m- tolualdehyde), three ketones (acetone, 2-butanone, and cyclohexanone), one unsaturated carbonyl (crotonaldehyde), and three dicarbonyls (gly oxal, methylglyoxal, and biacetyl). Another 19 carbonyls have been ten tatively identified including 11 low molecular weight (MW) and interme diate MW carbonyls (of which four may be due to reactions of ambient N O, NO2, and ozone with DNPH on the sampling cartridge), four C-4-C-6 d icarbonyls present at trace levels, and four high MW aliphatic carbony ls (C-15-C-18) Total carbonyl concentrations (4-h samples) averaged 22 ppb at the urban locations and 3.5 ppb at the background location and were highest (29 ppb) at the Azusa, CA, monitoring site that is downw ind of downtown Los Angeles. Formaldehyde (urban average 5.3 ppb), ace taldehyde, and acetone accounted for 24%, 18%, and 7%, respectively, o f the total carbonyls on a ppbv basis. The nine high MW carbonyls (C-8 -C-14) accounted for 11-14% of the total carbonyls. The acetaldehyde/f ormaldehyde concentration ratio averaged 0.75 at the urban locations. Ranking of the measured carbonyls with respect to removal of the hydro xyl radical showed acetaldehyde to be the most important followed by f ormaldehyde and nonanal. Diurnal and spatial variations in ambient car bonyls levels are briefly examined and appear to be consistent with bo th direct emissions and insitu formation during eastward transport ove r the urban area.