Impact of a large wildfire on water-soluble organic aerosol in a major urban area: the 2009 Station Fire in Los Angeles County

• 發表在: Atmospheric Chemistry and Physics
• Main Authors: A. Wonaschütz, S. P. Hersey, A. Sorooshian, J. S. Craven, A. R. Metcalf, R. C. Flagan, J. H. Seinfeld
• 格式: Article
• 語言: 英语
• 出版: Copernicus Publications 2011-08-01
• 在線閱讀: http://www.atmos-chem-phys.net/11/8257/2011/acp-11-8257-2011.pdf
• ISSN: 1680-7316; 1680-7324

This study examines the nature of water-soluble organic aerosol measured in Pasadena, CA, under typical conditions and under the influence of a large wildfire (the 2009 Station Fire). During non-fire periods, water-soluble organic carbon (WSOC) variability was driven by photochemical production processes and sea breeze transport, resulting in an average diurnal cycle with a maximum at 15:00 local time (up to 4.9 μg C m<sup>−3</sup>). During the Station Fire, primary production was a key formation mechanism for WSOC. High concentrations of WSOC (up to 41 μg C m<sup>−3</sup>) in smoke plumes advected to the site in the morning hours were tightly correlated with nitrate and chloride, numerous aerosol mass spectrometer (AMS) organic mass spectral markers, and total non-refractory organic mass. Processed residual smoke was transported to the measurement site by the sea breeze later in the day, leading to higher afternoon WSOC levels than on non-fire days. Parameters representing higher degrees of oxidation of organics, including the ratios of the organic metrics <i>m/z</i> 44:<i>m/z</i> 57 and <i>m/z</i> 44:<i>m/z</i> 43, were elevated in those air masses. Intercomparisons of relative amounts of WSOC, organics, <i>m/z</i> 44, and <i>m/z</i> 43 show that the fraction of WSOC comprising acid-oxygenates increased as a function of photochemical aging owing to the conversion of aliphatic and non-acid oxygenated organics to more acid-like organics. The contribution of water-soluble organic species to the organic mass budget (10th–90th percentile values) ranged between 27 %–72 % and 27 %–68 % during fire and non-fire periods, respectively. The seasonal incidence of wildfires in the Los Angeles Basin greatly enhances the importance of water-soluble organics, which has implications for the radiative and hygroscopic properties of the regional aerosol.