Integrated Laboratory and Field Characterization of Organic Carbon in PM2.5 Formed through Chemical Reactions John Offenberg1, Tadeusz Kleindienst1, Edward Edney1, Michael Lewandowski1, Mohammed Jaoui2 !U.S EPA/ORD/NERL'HEASD. 109 T.W. Alexander Dr., RTP, NC27711; 5 Alion Science and Technology, P.O. Box 12313, RTP, NC 27709 Abstract An integrated laboratory and field research program is underway at the National Exposure Research Laboratory (NERL) to characterize organic carbon in PM25 (particulate matter) formed through chemical reactions. Information from this study will provide critical data needed to improve the treatment of secondary organic aerosol (SOA) formation in the Community Multiscale Air Quality (CMAQ) model. In the laboratory portion, SOA-producing hydrocarbon precursors are irradiated in a photochemical reaction chamber in the presence of nitrogen oxide (NOx) and sulfur dioxide (S02). In these reactions, identifiable organic compounds indicative of the precursor gases are formed. These same compounds are then measured in field study samples to ensure that relevant chemical systems are being studied. In collaboration with the California Institute of Technology and the University of Antwerp, analytical methods and instruments are used to identify the products. Efforts are also underway with the Atmospheric Modeling Division (AMD) of NERL to incorporate findings from the field and laboratory measurements to improve the treatment of SOA within CMAQ. The project results should provide the Office of Air Quality Planning and Standards with critical data on important regulatory issues, among them (1) contributions of each SOA precursor to the PM2.5 concentration, (2) relative contributions of anthropogenic and biogenic hydrocarbons to ambient SOA concentrations, and (3) impacts of S02 reductions on SOA formation. This information will improve the treatment of SOA in the CMAQ model and help states evaluate control strategies for reducing ambient PM25. These results will support effective regulations and provide information that improves public health and reduces ecological impacts. Goals and Objectives Approach for Studies • Conduct field studies to measure the organic fraction of ambient PM2 5. Identify tracer compounds in the ambient samples, such as those that would be collected from the atmosphere depicted above. • Conduct laboratory experiments to identify reaction systems responsible for the observed tracer compounds. Use the NERL smog chamber to generate these atmospheres. Establish reaction mechanisms for SOA formation. • Conduct modeling studies to predict the formation and partitioning of SOA within PM2 5. • Collaborate with the AMD in NERL to incorporate the findings in CMAQ. Schematic of Approach for Implementation Studies Smog Chamber Results and Conclusions S02 Outputs SOA Tracers Effects of Pollutants Outcomes Atmospheric Models Types of Experiments Conducted Lab Irradiation Experiments Field Studies Toluene/NOx/S02 RTP, NC 2000 summer a-Pinene/NOx /Air + S02 RTP, NC 2003 /3-Pinene/NOx/Air Baltimore, MD2001 summer d-1 i m on e n e/NOx/Ai r Philadelphia, PA 2001 summer lsoprene/NOx/Air + SO? New York City, NY 2001 summer Toluene/a-Pinene/NOx + S02 Detroit, Ml 2004 summer a- Pi n en e//3- P i n e n e/d- li mon en e/N Oy lsoprene/a-Pinene/NOy Isoprene/a-Pinene/Toluene/NOx + S02 • Identify the major SOA precursors important in PM25 • Identify tracer compounds for the major SOA precursors • Determine reaction mechanisms for SOA formation • Aid AMD in NERL to improve treatment of SOA in CMAQ • Use the NERL smog chamber to generate atmospherically relevant air mixtures for exposure studies Experimental Methods • Irradiate individual aromatic and biogenic hydrocarbons in the presence of NOx and S02 in the NERL smog chamber and measure the SOA masses produced by the photooxidations. • Analyze chamber SOA samples using LC/MS, derivative-based GC/MS, Ion Trap MS, and MALDI methods to identify SOA tracer compounds. • Compare chamber composition and concentration data with model predictions whose formation mechanisms include contributions from gas-aerosol partitioning, acid catalyzed reactions, and polymer formation, and others. • Assess whether tracer concentrations can be used to determine contributions of SOA precursors to ambient PM2 5. 2003 RTP PM2.5 Concentrations Data • Smog chamber irradiations of biogenic hydrocarbons (emitted from trees and other vegetation) and aromatic hydrocarbons (emitted mainly from cars) show that these compound can be converted to SOA by chemical reactions. • For compounds such as isoprene and a-pinene, the addition of S02 increases the amount of SOA formed above that obtained in the absence of S02. • Laboratory results suggest that several chemical processes must be included in a model to explain SOA formation. The types of processes that appear to be important include (1) exchange of organic compounds between the gas and particle phases, often referred to as partitioning, (2) acid catalyzed reactions within the particle, (3) polymer formation, and possibly (4) cloud water reactions could be contributing to SOA formation. • Toluene, a-pinene, and isoprene SOA tracer compounds detected in ambient PM2 5 samples collected in the eastern USA indicate these emitted hydrocarbons are contributing to SOA. Analysis of field data suggests that SOA in the summer is significant, but decreases considerably in the colder seasons. • The figure below shows how the concentrations of the tracer compounds change with season. The isoprene tracer is only seen in the summertime, while the tracer compound for a-pinene is detected in the spring, summer, and fall. Levoglucosan, a primary product from wood combustion, is detected throughout the year but mainly during the winter and spring. Outputs, Outcomes and Future Directions • Continue comparing chamber concentrations and compositions of SOA formed with atmospherically relevant individual and mixtures of hydrocarbons irradiated in the presence of NOx and SO2 with model results for proposed SOA formation mechanisms. • Assess whether SOA yields in complex hydrocarbon mixtures are additive. • Work with AMD modelers to develop the CMAQ version of the PM chemistry model. • Results of the laboratory and field studies will used by AMD in the CMAQ model that will be available to the RPOs for State Implementation Plan modeling studies. • Some of the laboratory methods, developed under this program, will be used in EPA-NOAA collaborative research to assess the impact of N2O5 reactions on PM2.5 nitrate levels. 150 200 250 Julian Day 2003 Disclaimer: Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy. epascienceforum Your Health • Your Environment • Your Future ------- |