Light absorption by secondary organic aerosol from α-pinene: Effects of oxidants, seed aerosol acidity, and relative humidity

Authors

  • Chen Song,

    Corresponding author
    1. Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, Washington, USA
    2. Now at R. J. Reynolds Tobacco Company, Winston-Salem, North Carolina, USA
    • Corresponding author: C. Song, R. J. Reynolds Tobacco Company, 401 N. Main St, Winston-Salem, NC 27101, USA. (songc@rjrt.com)R. A. Zaveri, Pacific Northwest National Laboratory, MSIN K9-30, PO Box 999, Richland, WA 99352, USA. (rahul.zaveri@pnnl.gov)

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  • Madhu Gyawali,

    1. Department of Physics, University of Nevada Reno, Nevada System of Higher Education, Reno, Nevada, USA
    2. Now at Desert Research Institute, Nevada System of Higher Education, Reno, Nevada, USA
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  • Rahul A. Zaveri,

    1. Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, Washington, USA
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  • John E. Shilling,

    1. Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, Washington, USA
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  • W. Patrick Arnott

    1. Department of Physics, University of Nevada Reno, Nevada System of Higher Education, Reno, Nevada, USA
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Abstract

[1] It is well known that light absorption from dust and black carbon aerosols has a warming effect on climate while light scattering from sulfate, nitrate, and sea salt aerosols has a cooling effect. However, there are large uncertainties associated with light absorption and scattering by different types of organic aerosols, especially in the near-UV and UV spectral regions. In this paper, we present the results from a systematic laboratory study focused on measuring light absorption by secondary organic aerosols (SOAs) generated from dark α-pinene + O3 and α-pinene + NOx + O3 systems in the presence of neutral and acidic sulfate seed aerosols. Light absorption was monitored using photoacoustic spectrometers at four different wavelengths: 355, 405, 532, and 870 nm. Significant light absorption at 355 and 405 nm was observed for the SOA formed from α-pinene + O3 + NO3 system only in the presence of highly acidic sulfate seed aerosols under dry conditions. In contrast, no absorption was observed when the relative humidity was elevated to greater than 27% or in the presence of neutral sulfate seed aerosols. Organic nitrates in the SOA formed in the presence of neutral sulfate seed aerosols were found to be nonabsorbing, while the light-absorbing compounds are speculated to be aldol condensation oligomers with nitroxy organosulfate groups that are formed in highly acidic sulfate aerosols. Overall, these results suggest that dark α-pinene + O3 and α-pinene + NOx + O3 systems do not form light-absorbing SOA under typical atmospheric conditions.

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