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Published August 27, 1996 | Supplemental Material
Journal Article Open

Air Quality Model Evaluation Data for Organics. 2. C_1−C_(14) Carbonyls in Los Angeles Air


As part of a larger experiment that provides a comprehensive set of observations to be used for testing air quality models for organic air pollutant transport and reaction, ambient air samples have been collected using DNPH-coated C_(18) cartridges at four urban locations and one background 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 (glyoxal, methylglyoxal, and biacetyl). Another 19 carbonyls have been tentatively identified including 11 low molecular weight (MW) and intermediate MW carbonyls (of which four may be due to reactions of ambient NO, NO_2, and ozone with DNPH on the sampling cartridge), four C_4−C_6 dicarbonyls present at trace levels, and four high MW aliphatic carbonyls (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 downwind of downtown Los Angeles. Formaldehyde (urban average 5.3 ppb), acetaldehyde, and acetone accounted for 24%, 18%, and 7%, respectively, of 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/formaldehyde concentration ratio averaged 0.75 at the urban locations. Ranking of the measured carbonyls with respect to removal of the hydroxyl radical showed acetaldehyde to be the most important followed by formaldehyde and nonanal. Diurnal and spatial variations in ambient carbonyls levels are briefly examined and appear to be consistent with both direct emissions and in-situ formation during eastward transport over the urban area.

Additional Information

© 1996 American Chemical Society. Received for review October 12, 1995. Revised manuscript received March 14, 1996. Accepted April 26, 1996. We thank the 13 California Institute of Technology graduate students and staff who participated in air monitoring site operations for their assistance; William Bope (South Coast Air Quality Management District) for logistical support in Azusa, Long Beach, and Los Angeles; Lowell Ashbaugh (California Air Resources Board) and Gervaise McKay (Unisearch Associates) for logistical support in Claremont; and Peter Greene (Bank of America Environmental Analysis Center, California Institute of Technology) for advice regarding LC-diode array and MS analyses. Denise Velez prepared the draft and final versions of the manuscript. This research was supported by the Electric Power Research Institute under agreement RP3189-03, by the California Institute of Technology Center for Air Quality Analysis, and by internal R&D funds, DGA, Inc., Ventura, CA.

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