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SOA YIELDS AND ORGANIC PRODUCT DISTRIBUTION FROM NATURAL HYDROCARBON/NOX IRRADIATIONS
Citation:
Conver, T. S., T. E. Kleindienst, W. Li, C. D. McIver, E. W. Corse, AND E O. Edney. SOA YIELDS AND ORGANIC PRODUCT DISTRIBUTION FROM NATURAL HYDROCARBON/NOX IRRADIATIONS. Presented at 19th Annual AAAR Conference, St. Louis, MO, November 6-10, 2000.
Impact/Purpose:
1. Determine the secondary organic aerosol (SOA) yields of biogenic and aromatic hydrocarbons under real world concentration and relative humidity conditions.
2. Determine the organic composition of SOA from photooxidation of biogenic and aromatic compounds.
3. Measure the partitioning coefficients of atmospherically relevant semivolatile SOA.
4. Investigate the impact of the chemical composition of the organic fraction of the PM2.5 on the partitioning of SOA compounds.
5. Develop a first generation SOA chemistry module.
Description:
Secondary organic aerosol (SOA) typically comprises one-quarter to one-third of the ambient aerosol mass in summertime urban atmospheres. In tropospheric environments, the main precursors of SOA come from aromatic and natural hydrocarbons. Recent work by various investigators have begun to provide a quantitative basis for establishing reaction yields and speciation of SOA.
A laboratory system has been developed to investigate SOA formation and composition under highly controlled conditions. For this work, two laboratory chamber systems were used. The first is based on a 9 cubic meter all-Teflon chamber operated in a static mode and the second on an 11.3 cubic meter, Teflon-lined smog chamber operated in a dynamic mode. SOA products from the NOX-mediated photooxidations of a-pinene, b-pinene, d-limonene, and delta-carene were generated. Chamber conditions were set to ensure that extensive secondary gas-phase chemistry occurred. Under these conditions, nucleation of the oxidized mixture occurred. Particles size and volume distributions were measured during the irradiation using a scanning mobility particle sizer. These measurements suggest that particle formation occurs before a substantial ozone concentration is generated in the chamber. SOA yield were measured from organic carbon measurements of 24-h quartz filter collections and the mass of reacted hydrocarbon. These measurements used carbon-based and extractable XAD denuders minimize filter artifacts.
Organic aerosol from the NOX irradiations was also collected on Zefluor filters and extracted for analysis of individual compounds. Derivatization techniques were used to classify and identify specific products formed in SOA. Since many of the products are expected to be semivolatile, XAD denuders were used to study the gas-aerosol partitioning. Comparisons will be made between the products formed in these systems with those reported for the ozone-natural hydrocarbon reactions.
The U.S. Environmental Protection Agency through its Office of Research and Development funded and collaborated in the research described here (Contract 68D5-0049 with ManTech Environmental Technology, Inc.). It has been subjected to Agency review and approved for publication.