Measuring and modeling the concentrations of individual organic compounds in the urban atmosphere

by Fraser, Matthew Paul

Abstract (Summary)
Field experiments and atmospheric models are used to explore the relationships between source emissions and ambient air quality for individual organic compounds. Measurements are made at a 5-station air monitoring network in the Los Angeles area during a severe photochemical smog episode. Air samples taken in stainless steel canisters are analyzed for 141 volatile organic compounds by GC/FID, GC/ECD and GC/MS; PAN and PPN are measured by GC/ECD; 82 vapor-phase semi-volatile organics are analyzed by GC/MS after collection on polyurethane foam, and 103 particulate organic compounds are determined by GC/MS. Twenty-three carbonyls are quantified. It is discovered that the high molecular weight carbonyls collectively are as important to atmospheric reactivity as formaldehyde or acetaldehyde individually. Organic compounds concentrations reflect recent changes in gasoline composition, show the decline in alkenes and aromatics concentrations due to atmospheric reactivity while oxy-PAH and nitroaromatics concentrations increase due to formation by atmospheric reactions over downwind transport across southern California. Low molecular weight aliphatic dicarboxylic acids in the air at San Nicolas Island upwind of Los Angeles are found at 44%-76% of urban concentrations, indicating that these compounds are contributed in part by long distance transport, by marine sources, or by oxidation of background biogenic hydrocarbons. The emissions rates of 221 vapor-phase, semi-volatile and particulate organic compounds from motor vehicle traffic are measured in a Los Angeles roadway tunnel. Carbon monoxide and organic vapor emissions are found to be much higher than current governmental estimates. Petroleum biomarlcers (e.g. hopanes and steranes) emissions rates are measured and used to trace motor vehicle exhaust particles in the urban atmosphere. Elevated ammonia emissions apparantly from three-way catalyst-equipped vehicles were discovered during the highway tunnel experiment. These previously undocumented NH3 emissions have the potential to increase atmospheric NH4NO3 aerosol concentrations. An Eularian photochemical airshed model is adapted to simultaneously predict the concentrations of nearly 100 individual gas phase, semi-volatile and particle phase organic compounds directly from data on source emisssions. Most organic compounds concentrations are predicted within the correct order of magnitude over 6 orders of magnitude difference in concentrations between the species studied.
Bibliographical Information:

Advisor:Glen Rowan Cass

School:California Institute of Technology

School Location:USA - California

Source Type:Master's Thesis

Keywords:environmental science and engineering


Date of Publication:01/07/1998

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