NERL Research Abstract EPA's National Exposure Research Laboratory GPRA Goal 1 - Clean Air APM # 443 Significant Research Findings Atmospheric Chemistry of Secondary Organic Aerosol Formation Research The overall objective of this research is to determine the key chemical and Approach physical processes that control the yield and chemical composition of the secondary organic aerosol (SOA) component of particulate matter (PM2 5) from atmospheric transformations of aromatic compounds, biogenic hydrocarbons, and atmospherically relevant mixtures including synthetic automobile exhaust. The SOA yield is the amount of organic aerosol produced per unit hydrocarbon reacted—a critical parameter needed to develop cost-effective control strategies for SOA formation. To generate this information, a smog chamber system was developed for simulating SOA formation under near-ambient conditions. The smog chamber was used to irradiate selected hydrocarbons in the presence of nitrogen oxides to assess the impact of environmental parameters such as relative humidity on the yield and chemical composition of SOA. The hydrocarbon systems investigated to date include toluene,/^-xylene, 1,3,5- trimethylbenzene, and synthetic automobile exhaust. Results of the laboratory study clearly demonstrated that aromatic compounds emitted into the atmosphere contribute to SOA formation through atmospheric transformation to form oxidation products that are partially absorbed into the organic films on pre-existing PM2 5. The SOA yields were found to be strongly influenced by the total mass of organic compounds present on the aerosol, but were not affected significantly by typical daytime relative humidity. Furthermore, the laboratory results demonstrated that SOA compounds from aromatic compounds are far less effective in taking up liquid water that contributes to regional haze than sulfate and nitrate compounds commonly found in PM2 5. The SOA chemical composition studies, which represent the first investigation of this type, are consistent with the formation of multi- functional oxygenated compounds. Finally, it was demonstrated that as much as 75% of the SOA from synthetic automobile exhaust could be explained by the aromatic content of the exhaust. These results and others obtained in the study will serve as the foundation for building a chemical mechanism to be used in an air quality model to predict the contribution of SOA formation to Results and Implications National Exposure Research Laboratory - September 2000 ------- ambient PM2 5 levels. These predictions will be used to target specific sources of SOA for emission reductions. Research The PM chemistry laboratory program was conducted by a team of NERL staff Collaboration scientists along with support from ManTech Environmental Technology, Inc. *tu1l1. . This research has been presented at several conferences and in the following Publications . , , . articles and manuscripts. Kleindienst, T.E., Smith, D.F., Li, W., Edney, E.O., Driscoll, D.J., Speer, R.E., Weathers, W.S. Secondary organic aerosol formation from the oxidation of aromatic hydrocarbons in the presence of dry submicron ammonium sulfate aerosol. Atmospheric Environment 33: 3669-3681, 1999. Edney, E.O., Driscoll, D.J., Speer, R.E., Weathers, W.S., Kleindienst, T.E., Li, W., Smith, D.F. Impact of aerosol liquid water on secondary aerosol yields of irradiated toluene/propylene/NOx/ (NH4)2S04/air mixtures. Atmospheric Environment 34: 3907- 3919, 2000. Edney, E.O., Driscoll, D.J., Weathers, W.S., Kleindienst, T.E., Conver, T.S., Mclver, C.D., Li, W. Formation of polyketones in irradiated toluene/propylene/NOx/air mixtures. Aerosol Science & Technology. Submitted. Kleindienst, T.E., Li, W., Edney, E.O., Driscoll, D.J., Speer, R.E., Weathers, W.S., Tejada. Secondary organic aerosol formation from the irradiation of simulated automobile exhaust. Journal of Air & Waste Management Association. Submitted. Although this research has led to a significant improvement in the understanding of the SOA formation from aromatic compounds, additional research is required to investigation other significant sources of SOA including biogenic hydrocarbons. Experiments similar to those conducted for aromatic compounds are underway for biogenic hydrocarbons. Laboratory studies are planned to assess the impact of the organic composition of pre-existing PM2 5 on the SOA yields of aromatic and biogenic compounds. Furthermore, during the summer of 2000, ambient PM2 5 samples will be collected and analyzed for the presence of multifunctional oxygenates. Questions and inquiries on NERL's PM chemistry research can be directed to: Edward O. Edney, Ph.D. U.S. Environmental Protection Agency National Exposure Research Laboratory (MD-84) Research Triangle Park, NC 27711 Phone: (919)541-3905 E-mail: edney.edward@epa.gov Future Research National Exposure Research Laboratory - September 2000 ------- |