|
Atmos. Chem. Phys. Discuss., 11, 17071-17125, 2011
www.atmos-chem-phys-discuss.net/11/17071/2011/ doi:10.5194/acpd-11-17071-2011 © Author(s) 2011. This work is distributed under the Creative Commons Attribution 3.0 License. |
Origins and composition of fine atmospheric carbonaceous aerosol in the Sierra Nevada Mountains, California
1Department of Environmental Science, Policy and Management, University of California, Berkeley, CA, 94720, USA
2Aerosol Dynamics Inc., Berkeley, CA 94710, USA
3Departments of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA
4Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, 80309, USA
5Department and Chemistry and Biochemistry, University of Colorado, CO, 80309, USA
6NOAA Earth System Research Laboratory, Boulder, CO 80305, USA
7Energy, Environmental and Chemical Engineering, Washington University, St. Louis, MO 63130, USA
8Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
9Department of Chemistry, University of Aarhus, Aarhus C, 8000, Denmark
10Department of Chemistry, California Institute of Technology, Pasadena, CA 91125, USA
11Departments of Environmental Science and Engineering and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
*now at: Alion Science and Technology, EPA Office of Research and Development, EPA Research and Development, Research Triangle Park, NC, USA
**now at: California Air Resources Board, Sacramento, CA, USA
***now at: Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
Abstract. In this paper we report chemically resolved measurements of organic aerosol (OA) and related tracers during the Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX) at the Blodgett Forest Research Station, California. OA contributed the majority of the mass to the fine atmospheric particles and was predominately oxygenated (OOA). The highest concentrations of OA were during sporadic wildfire influence when aged plumes were impacting the site. In situ measurements of particle phase molecular markers were dominated by secondary compounds and could be categorized into three factors or sources: (1) aged biomass burning emissions and oxidized urban emissions, (2) oxidation products of temperature-driven local biogenic emissions and (3) local light-driven emissions and oxidation products. There were multiple biogenic components that contributed to OA at this site whose contributions varied diurnally, seasonally and in response to changing meteorological conditions, e.g., temperature and precipitation events. Concentrations of isoprene oxidation products were larger when temperatures were higher due to more substantial emissions of isoprene and enhanced photochemistry. Methyl chavicol oxidation contributed similarly to OA during both identified meteorological periods. In contrast, the abundances of monoterpene oxidation products in the particle phase were greater during cooler conditions, even though emissions of the precursors were lower. Following the first precipitation event of the fall the abundances of the monoterpene oxidation products increased dramatically, although the mechanism is not known. OA was correlated with the anthropogenic tracers 2-propyl nitrate and carbon monoxide (CO), consistent with previous observations, while being comprised of mostly non-fossil carbon (>75 %). The correlation between OA and an anthropogenic tracer does not necessarily identify the source of the carbon as being anthropogenic but instead suggests a coupling between the anthropogenic and biogenic components in the air mass that might be related to the source of the oxidant and/or the aerosol sulfate. Observations of organosulfates of isoprene and α-pinene provided evidence for the likely importance of aerosol sulfate in spite of neutralized aerosol. This is in contrast to laboratory studies where strongly acidic seed aerosols were needed in order to form these compounds. These compounds together represented only a minor fraction (< 1 %) of the total OA mass and suggest that other mechanisms, e.g., NOx enhancement of oxidant levels, are more likely to be responsible for the majority of the anthropogenic enhancement of biogenic secondary organic aerosol observed at this site.
Citation: Worton, D. R., Goldstein, A. H., Farmer, D. K., Docherty, K. S., Jimenez, J. L., Gilman, J. B., Kuster, W. C., de Gouw, J., Williams, B. J., Kreisberg, N. M., Hering, S. V., Bench, G., McKay, M., Kristensen, K., Glasius, M., Surratt, J. D., and Seinfeld, J. H.: Origins and composition of fine atmospheric carbonaceous aerosol in the Sierra Nevada Mountains, California, Atmos. Chem. Phys. Discuss., 11, 17071-17125, doi:10.5194/acpd-11-17071-2011, 2011.