AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Secondary Organic Aerosol Formation in a Forested Environment with Limited Anthropogenic Influence
ALEX K. Y. LEE, Jonathan Abbatt, W. Richard Leaitch, Shao-Meng Li, John Liggio, Annie-Marie Macdonald, Steve Sjostedt, Jeremy Wentzell, University of Toronto
Abstract Number: 18 Working Group: Aerosol Chemistry
Abstract A biogenic secondary organic aerosol (BSOA) episode was observed in a forested mountain region at Whistler, British Columbia, providing a unique opportunity to investigate BSOA formation in a forested environment without significant anthropogenic influence. Positive matrix factorization of aerosol mass spectrometry (AMS) measurements identified two BSOA factors (namely BSOA-1 and BSOA-2), which were predominantly generated by gas-phase oxidation of monoterpenes and perhaps sesquiterpenes. The diurnal cycles of BSOA-1 and 2 observed at the later period of the campaign can be explained by gas-particle partitioning of BSOA materials in response to ambient temperature and the relative importance of different oxidation mechanisms between day and night. Gas-phase ozonolysis at night will be one of the production pathways of BSOA-1, whereas BSOA-2 consisted of products formed also through gas-phase oxidation by OH radical and ozone during the day. In addition, BSOA-1 was likely more volatile than BSOA-2 due to a smaller contribution of organic acids, resulting in a decreased concentration of BSOA-1 during the day when temperatures are higher. The mass spectra of BSOA-1 and 2 have much higher values of the mass fraction of m/z 91 (f91) compared to the aged background organic aerosol, suggesting that f91 can be used as a tracer to evaluate BSOA formation pathways. A comparison between our observations and previous laboratory investigations highlights the potential importance of gas-phase formation of BSOA-2 type materials that may not be captured in smog chamber experiments, perhaps due to the wall loss of gas-phase intermediate products.