ARB Research Seminar
This page updated July 26, 2013
Oxygenated Organics in the Ambient Environment
M. Judith Charles, Ph.D., Department of Environmental Toxicology, University of California, Davis
July 17, 2003
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA
The reaction of anthropogenic and biogenic hydrocarbons with hydroxyl radicals (OH) and ozone yields oxygenated species including carbonyls and multi-functional carbonyls that play an important role in organic aerosol formation and in the oxidizing capacity of the atmosphere. Due to their polar nature, oxygenated organics can be lost from the gas-phase via partitioning to clouds, fog, rain, or aerosols, and wet- deposition. The effect of these processes on the atmospheric budget of organic carbon is unknown and needs to be quantified. To address this issue, and to evaluate models that predict the role of oxygenated volatile organic compounds (OVOC) in tropospheric chemistry and ozone and aerosol formation, my laboratory develops analytical approaches. These approaches are used to measure oxygenated organics in the ambient atmospheric environment.
We began by using impingers for sampling in concert with derivatization and gas chromatography/ion trap mass spectrometry to unambiguously identify carbonyls and multifunctional carbonyls in air. Carbonyls are derivatized with O- (2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA), and the hydroxyl and carboxyl groups on multi-functional carbonyls (e.g., hydroxy carbonyls and oxo-acids) are further derivatized with bis (trimethylsilyl)-trifluoroacetamide (BSTFA). These techniques were used to identify carbonyls in Asuza, California as part of the 1997 Southern California Oxidant Study (SCOS). In this work, we demonstrated the potential of the method to measure water-soluble carbonyls for which no or little ambient air data exist, and provided the first report of hydroxyacetone and 3-hydroxy-butanone in the ambient atmosphere. In another field sampling campaign in Blodgett Forest, California, we measured carbonyl and multifunctional carbonyl photooxidation products of isoprene (glyoxal, methylglyoxal, hydroxyacetone and glycolaldehyde) and MBO (2-hydroxy-2-methyl-propanal; 2-HMPR) at ppt levels. We were the first to identify the MBO + OH. reaction product, 2-HMPR in the ambient environment. In our most recent work, in collaboration with Allen Goldstein, UC Berkeley, we measured isoprene, MBO, and their first-, second- and third-generation photooxidation near the Blodgett Forest Research Station in August and September, 2000. Quantification of the source apportionment demonstrated that photooxidation of anthropogenic precursors contribute significantly to the mixing ratios of glycolaldehyde and hydroxyacetone in this rural environment. Further research into the photochemistry and yields of carbonyl and multifunctional carbonyls products of hydrocarbon photooxidation is needed in order for the models to accurately predict their role in tropospheric chemistry.
Professor Judith Charles has been a faculty member in the Department of Environmental Toxicology at UCD since 1996. Before joining UCD's toxicology department, she was an Associate Professor with the Department of Environmental Sciences and Engineering School of Public Health, University of North Carolina at Chapel Hill. Her professional interests are very wide and range from the atmospheric chemistry (ozone and particulate formation) of anthropogenic and biogenic hydrocarbons to the health effects of endocrine disruptors (organochlorines) in human populations.