Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 11, 10219-10241, 2011
© Author(s) 2011. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research Article
12 Oct 2011
Origins and composition of fine atmospheric carbonaceous aerosol in the Sierra Nevada Mountains, California
D. R. Worton1,2, A. H. Goldstein1,3, D. K. Farmer4,5, K. S. Docherty4,5,*, J. L. Jimenez4,5, J. B. Gilman4,6, W. C. Kuster6, J. de Gouw4,6, B. J. Williams7, N. M. Kreisberg2, S. V. Hering2, G. Bench8, M. McKay1,**, K. Kristensen9, M. Glasius9, J. D. Surratt10,***, and J. H. Seinfeld11
1Department of Environmental Science, Policy and Management, University of California, Berkeley, CA, 94720, USA
2Aerosol Dynamics Inc., Berkeley, CA, 94710, USA
3Department 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 of Chemistry and Biochemistry, University of Colorado, Boulder, 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 from 15 August–10 October 2007. 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 along with gas phase compounds could be categorized into six factors or sources: (1) aged biomass burning emissions and oxidized urban emissions, (2) oxidized urban emissions (3) oxidation products of monoterpene emissions, (4) monoterpene emissions, (5) anthropogenic emissions and (6) local methyl chavicol 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 during the first half of the campaign (15 August–12 September) due to more substantial emissions of isoprene and enhanced photochemistry. The oxidation of methyl chavicol, an oxygenated terpene emitted by ponderosa pine trees, contributed similarly to OA throughout the campaign. In contrast, the abundances of monoterpene oxidation products in the particle phase were greater during the cooler conditions in the latter half of the campaign (13 September–10 October), even though emissions of the precursors were lower, 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 although acidic plumes might have played a role upwind of the site. 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, which may be the result of the neutralized aerosol at the site or because only a small number of organosulfates were quantified. The low contribution of organosulfates to total OA suggests that other mechanisms, e.g. NOx enhancement of oxidant levels, are likely 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., 11, 10219-10241, doi:10.5194/acp-11-10219-2011, 2011.
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