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SMOG CHAMBER STUDIES OF SECONDARY ORGANIC AEROSOLS FROM IRRADIATED HYDROCARBONS UNDER AMBIENT CONDITIONS
Citation:
Edney, E O., E C. Swartz, D J. Driscoll, T. E. Kleindienst, W. Li, T. S. Conver, AND C. D. McIver. SMOG CHAMBER STUDIES OF SECONDARY ORGANIC AEROSOLS FROM IRRADIATED HYDROCARBONS UNDER AMBIENT CONDITIONS. Presented at American Geophysical Union Fall Meeting, San Francisco, CA, December 13-17, 1999.
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:
Understanding the physics and chemistry of aerosols is fundamental to evaluating health risks and developing and evaluating atmospheric models. However, as noted in a recent NRC report only about 10% of the organics in PM2.5 have been identified. A significant portion of the unidentified fraction could be polar compounds formed from the oxidation of aromatic and biogenic hydrocarbons that are taken up by pre-existing aerosols. Secondary organic aerosols (SOA), formed when products of gas-phase reactions partition into the aerosol phase, have been found to represent up to 70% of the organic mass. Thus a comprehensive understanding of the key chemical and physical parameters that control their formation under ambient conditions is required.
Information such as secondary organic aerosol (SOA) yields at near ambient concentrations conditions in the absence and presence of aqueous films, the impact of deposited organics on the hydroscopic properties of the aerosol, and chemical composition of the organic aerosol are needed to develop and evaluate models for tropospheric aerosols. A flow chamber was developed for generating secondary organic and inorganic aerosols by irradiating mixtures of hydrocarbons (HC), oxides of nitrogen (NOx) in air in the presence or absence of preexisting inorganic aerosols in the form of (NH4)2 S04. The chamber was designed so relative humidity could be controlled (20-80% R.H.) and near ambient concentrations could be used. Steady state gas phase concentrations of HC, NOx, 03, PAN, carbonyl compounds, organic acids, and HN03 were measured. The exposed aerosol were analyzed for their size, mass, inorganic composition including liquid water concentrations and total organic carbon contents. Measurements of the SOA yield were made frown organic carbon measurements of 24 hour filter collections and the mass of reacted hydrocarbon. The secondary organic aerosol yield of 1.59% was found for toluene at an organic aerosol concentration of 8.2 ugm-3, 1.09% for p-xylene at 6.4 ugm-3, and 0.41 % for 1,3,5-trimethyl benzene at 2.0 ugm-3. In general, these results agree with those reported by Odum et al. and appear to be consistent with the gas-aerosol partitioning theory developed by Pankow.
This work has been funded wholly or in part by the United States Environmental Protection Agency under Contract 68-D5-0049 to ManTech Environmental Technology, Inc.. It has been subjected to Agency review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommended use.