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PRIMARY AND SECONDARY CONTRIBUTIONS TO AMBIENT PM IN THE MIDWESTERN UNITED STATES
Citation:
LEWANDOWSKI, M., MOHAMMAD JAOUI, J. H. OFFENBERG, T. E. KLEINDIENST, E. O. EDNEY, R. J. SHEESLEY, AND J. J. SCHAUER. PRIMARY AND SECONDARY CONTRIBUTIONS TO AMBIENT PM IN THE MIDWESTERN UNITED STATES. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 42(9):3303-3309, (2008).
Impact/Purpose:
1. Conduct laboratory studies with scientists from Caltech, the University of Antwerp, and the NOAA Aeronomy Laboratory to improve treatments of SOA Chemistry and N2O5 chemistry in CMAQ.
2. Analyze ambient PM2.5 samples in Research Triangle Park, NC, Detroit, MI and Pasadena, CA and when available compare field data with CMAQ predictions obtained from AMD.
3. In 2005 recommend improvements to AMD for the treatment of SOA chemistry in CMAQ.
4. By the end of FY06, deliver an improved SOA chemistry model to AMD who will incorporate the model into CMAQ.
5. By the end of 2007, deliver an improved N2O5 chemistry model to AMD who will incorporate the model into CMAQ.
Description:
Ambient PM2.5 samples were collected in five Midwestern US cities throughout 2004: East St. Louis, Illinois; Detroit, Michigan; Cincinnati, Ohio; Bondville, Illinois; and Northbrook, Illinois. Monthly composites were analyzed using chemical derivatization coupled with GC-MS analysis to estimate the contributions of several sources to the total ambient organic carbon. A chemical mass balance (CMB) approach was used to estimate contributions from several primary sources. An additional, organic tracer-based technique was employed to estimate secondary contributions, including secondary organic carbon derived from isoprene, a-pinene, β-caryophyllene, and toluene. The sum of these contributions was compared with the total. Organic carbon measured at each sampling site, and reasonable carbon mass balances were observed for four of the five sites. In Bondville, Northbrook, Cincinnati, and Detroit, a strong correlation was observed between the sum of the estimated primary and secondary contributions and the measured organic carbon (R2 = 0.73). The estimated secondary organic carbon concentrations were observed to vary considerably with season, with the strongest contributions coming from isoprene and a-pinene during the summer. While further research is required, there is some evidence the contribution estimates for a-pinene, β-caryophyllene, and toluene SOC may to some degree represent the contributions from the broader classes of monoterpenes, sesquiterpenes, and aromatics.