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SECONDARY ORGANIC AEROSOL FORMATION FROM THE OXIDATION OF AROMATIC HYDROCARBONS IN THE PRESENCE OF DRY SUBMICRON AMMONIUM SULFATE AEROSOL
Kleindienst, T. E., D. F. Smith, W. Li, E O. Edney, D J. Driscoll, R E. Speer, AND W S. Weathers. SECONDARY ORGANIC AEROSOL FORMATION FROM THE OXIDATION OF AROMATIC HYDROCARBONS IN THE PRESENCE OF DRY SUBMICRON AMMONIUM SULFATE AEROSOL. ATMOSPHERIC ENVIRONMENT 33(22):3669-3681, (1999).
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.
A laboratory study was conducted to examine formation of secondary organic aerosols. A smog chamber system was developed for studying gas-aerosol interactions in a dynamic flow reactor. These experiments were conducted to investigate the fate of gas and aerosol phase compounds generated from hydrocarbon-nitrogen oxide (HC/NOJ mixtures irradiated in the presence of fine ( < 2.5 um) particulate matter. The goal was to determine to what extent photochemical oxidation products of aromatic hydrocarbons contribute to secondary organic aerosol formation through uptake on pre-existing inorganic aerosols in the absence of liquid water films. Irradiations were conducted with toluene, p-xylene, and 1,3,5-trimethylbenzene in the presence of N0x and ammonium sulfate aerosol, with propylene added to enhance the production of radicals in the system. The secondary organic aerosol yields were determined by dividing the mass concentration of organic fraction of the aerosol collected on quartz filters by the mass concentration of the aromatic hydrocarbon removed by reaction. The mass concentration of the organic fraction was obtained by multiplying the measured organic carbon concentration by 2.0, a correction factor that takes into account the presence of hydrogen, nitrogen, and oxygen atoms in the organic species. The mass concentrations of ammonium, nitrate, and sulfate concentrations as well as the total mass of the aerosols were measured. A reasonable mass balance was found for each of the aerosols. The largest secondary organic aerosol yield of 1.59 ? 0.40% was found for toluene at an organic aerosol concentration of 8.2 um-3, followed by 1.09 ? 0.27% for p-xylene at 6.4 ug m-3, and 0.41 ? 0.10% for 1,3,5-trimethylbenzene at 2.0 ug m-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. The presence of organic in the aerosol did not affect significantly the hygroscopic properties of the aerosol.
The reserach described in this paper has been funded wholely by the US Environmental Protection Agency under Contract 68-D5-0049 to ManTech Environmental Technology, Inc. It has not been subject to Agency review. Mention of trade names or commercial products does not constitute endorsement or recommended use.