Department of Environmental Sciences

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Seminar Abstracts
Environmental Sciences Seminar Abstract            

  To What Extent Can Biogenic Secondary Organic Aerosol be Controlled?
Ann Marie Carlton
EPA, Triangle Park, NC

Anthropogenic pollution facilitates conversion of naturally emitted volatile organic compounds (VOCs) to the particle phase, enhancing biogenic secondary organic aerosol (SOA) in the atmosphere. 'Biogenic' SOA is a product of natural precursor VOCs as well as anthropogenic constituents. Anthropogenic pollution increases concentrations of oxidants (O3, OH, NO3) that convert biogenic VOCs to semi-volatile, condensable, SOA-contributing species. Furthermore, increases in concentrations of primary organic matter facilitate condensation of semi-volatile biogenic species to the particle phase. Therefore, a portion of biogenic SOA can be attributed to anthropogenic emissions and may be controllable. Direct measurement of this component is not possible, but it can be estimated through modeling.

To test the contribution of anthropogenic pollution to biogenic SOA, CMAQ model simulations were conducted for the continental U.S. (August 18 - September 4) using a recently developed SOA module that includes several biogenic SOA precursors: isoprene, sesquiterpenes, monoterpenes. Biogenic SOA formation pathways include oxidation of volatile species to semi-voltaile products followed by gas-to-particle partitioning, oligomerization and in-cloud processes. CMAQ simulations were conducted with and without anthropogenic emissions. The relative contributions of individual pollution classes (i.e., NOx, VOCs, NH3, SO2 and primary organic particulate matter) were also evaluated by removing the individual components from the emissions, one at a time. Model results demonstrate a strong influence of anthropogenic pollution on predicted 'biogenic' SOA concentrations. In these simulations, approximately 40% of biogenic SOA in the eastern U.S. can be controlled. Total biogenic SOA was most sensitive to primary organic particulate matter emissions, suggesting regulations aimed at PM emissions could reduce biogenic SOA by ~20%. Individual biogenic SOA species exhibit different responses to anthropogenic emission reductions. Cloud-produced SOA, which has biogenic and anthropogenic VOC precursors was most sensitive to NOx reductions.

Last updated: 02/20/2009