United States Environmental Protection Agency Office of Research and Development National Exposure Research Laboratory FY02 Research Abstract Government Performance Results Act (GPRA) Goal 1 APM24 Significant Research Findings: Ambient Field Study and Smog Chamber Investigations of Formation of Secondary Organic Aerosol from Complex Mixtures of Hydrocarbons Scientific Results of epidemiology studies indicate exposure to ambient Particulate Problem and Matter (PM) with aerodynamic diameters less than 2.5 |im (PM2 5) is Policy Issues correlated with daily mortality and morbidity rates. However, to date the compound(s) responsible for the adverse health effects have not been established, which is due in some part to the fact that the chemical composition of ambient PM2 5 has not been fully characterized, in particular its organic fraction. To address this issue, the U.S. Environmental Protection Agency (EPA) National Exposure Research Laboratory (NERL) is carrying out laboratory and field studies to determine the chemical composition and concentration of PM2 5. In these investigations, special emphasis is placed on assessing the impact of secondary organic aerosol (SOA) formation on ambient PM2 5 concentrations. Although PM2 5 is directly emitted into the troposphere, it is also introduced by SOA formation where high volume reactive volatile hydrocarbons, including aromatic hydrocarbons in automobile exhaust and biogenic hydrocarbons released by vegetation, undergo atmospheric transformations forming oxidation products that contribute to the PM2 5 mass concentration by new particle formation and/or uptake to pre-existing PM2 5. The results of the laboratory and field studies will be used to develop and evaluate a PM chemistry model, an FY04 Annual Performance Measure (APM) that is the major output of the PM chemistry program. The chemistry model will be used by EPA and the States to predict, for a varity of emission scenarios, the ambient concentrations and compositions of real world PM2 5 containing inorganic salts and acids, organic compounds and liquid water. The status of two of the studies and a summary of some of the significant findings, including those of a field study conducted to identify in ambient PM2 5 polar organic compounds, some of which are due to SOA formation, are presented. Understanding SOA and the contributions of biogenic and anthropogenic sources is of critical importance as EPA is working to National Exposure Research Laboratory — November 2002 ------- develop implementation plans with the States. Research Under this APM, (1) a short term field study was carried out to chemically Approach characterize the organic and inorganic composition of ambient PM2 5 and (2) a series of smog chamber irradiations of atmospherically relevant mixtures of biogenic and anthropogenic hydrocarbons were conducted to develop a data base that will be used to evaluate the PM chemistry model. The objective of the short term field study, carried out in Research Triangle Park, North Carolina during the summer of 2000, was to identify classes of polar oxygenates in PM2 5, including SOA PM2 5, containing carbonyl and/or hydroxyl functional groups and, to the extent possible, determine the individual particle-bound oxygenates that make up each class. Although there is some evidence that in certain locations such compounds may make up more than 75% of the organic fraction of PM2 5, there have been few attempts to identify these compounds in ambient PM2 5. During this field study, PM2 5 samples were collected and then analyzed for their mass, inorganic and organic composition, with special emphasis placed on identifying polar multifunctional organic compounds. The smog chamber program involved irradiating a wide range of atmospherically relevant mixtures of hydrocarbons and measuring their SOA yields. The chamber PM2 5 concentrations were monitored by measuring the volume distribution using a scanning mobility particle sizer. The data base of smog chamber results will be used mainly to evaluate the PM chemistry model, an FY04 APM. Results and The results of the summertime field study showed the PM2 5 mass Implications concentrations in Research Triangle Park, North Carolina ranged between 12 and 30 |ig m"3, with an average mass composition of 28% sulfate, 6% nitrate, 12% ammonium, 39% organic carbon compound, 2% elemental carbon, and 12%) liquid water at a relative humidity of 43%>. Chemical analyses revealed that as much as 90%> of the organic fraction was polar in nature. Infrared analysis of the PM2 5 was also consistent with the presence of significant levels of polar carbonyl and hydroxyl functional groups. The polar nature of the organic fraction was further supported by the observation that about 20%> of the liquid water concentrations was associated with the organic fraction of PM2 5. The importance of polar multifunctional oxygenates in the PM2 5 is also supported by mass spectra data that were consistent with the presence of a wide range of classes of polar oxygenates, among them oxo monocarboxylic acids, trihydroxy monocarboxylic acids, dihydroxy dicarboxylic acids, hydroxy dicarboxylic acids, normal dicarboxylic acids, oxo dicarboxylic acids, methoxy dicarboxylic acids, tricarboxylic acids, triols, and SOA products of a-pinene and toluene. In particular, five secondary organic aerosol compounds, observed in a smog chamber National Exposure Research Laboratory — November 2002 ------- irradiation of an a-pinene/NOx/air mixture were detected in ambient PM2 5, thus providing new biomarkers for identifying the contributions of biogenic hydrocarbons to PM2 5 concentrations by SOA formation. The data base of 24 smog chamber experiments will be used (1) to evaluate the PM chemistry model (FY04 APM 222), a critical tool for evaluating control strategies for reducing ambient PM2 5 concentrations, (2) to assess the relative contributions of anthropogenic and biogenic hydrocarbons to SOA formation, and (3) to determine the impact of control strategies for reducing SOA formation on ambient ozone concentrations. In each experiment, the concentrations of the individual compounds that made up the atmospherically relevant mixture of anthropogenic and biogenic hydrocarbons were measured as a function of time along with the concentrations of NOx compounds and PM2 5. The data base also includes, for each smog chamber experiment, concentration profiles for reaction products that included ozone, formaldehyde, acetaldehyde, additional carbonyl and dicarbonyl compounds, nitric acid, and peroxyacetyl nitrate. The PM chemistry laboratory program was conducted by a team of NERL scientists along with support from ManTech Environmental Technology, Inc., Dr Simon Clegg of the University of East Anglia, UK and Dr Lee Bartolotti of the North Carolina Supercomputing Center. This research has been presented at several conferences and in the following manuscripts: Edney, E.O., Kleindienst, T.E., Conver, T.S., Mclver, C.D., Speer, R.E., and Weathers, W.S. (2002). "Polar Organic Oxygenates in PM2 5 at a Southeastern Site in the United States." (Submitted to Atmospheric Environment). Speer, R.E., Edney, E.O., Kleindienst, T.E., (2002). "Determination of aerosol bound liquid water in ambient PM2 5." (In Press, Journal of Aerosol Science). Kleindienst, T.E., Edney, E.O., Corse, E.W., Li, W. (2002). "Secondary Organic Aerosol Formation from the Photooxidation of Complex Hydrocarbon Mixtures." (To be submitted to Environmental Science and Technology). Future Research Although the current research has led to a significant improvement in the understanding of formation of PM2 5 in the troposphere, further research is required. In particular, some additional laboratory experiments and field studies using more advanced analytical methods are needed to identify and quantify the organic compounds in PM2 5, critical information required to develop the PM chemistry model. Research Collaboration and Publications National Exposure Research Laboratory — November 2002 ------- Contacts for Questions and inquiries on NERL's PM Chemistry Research can be directed Additional Information Edward O. Edney, Ph.D. US EPA, Office of Research and Development National Exposure Research Laboratory (MD-84) Research Triangle Park, NC 27711 Phone: 919/541-3905 E-mail: edney.edward@epa.gov National Exposure Research Laboratory — November 2002 ------- |