Impact of a large wildfire on water-soluble organic aerosol in a major urban area: The 2009 station fire in Los Angeles County

A. Wonaschütz, S. P. Hersey, A. Sorooshian, J. S. Craven, A. R. Metcalf, R. C. Flagan, J. H. Seinfeld

Research output: Contribution to journalArticle

47 Scopus citations

Abstract

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 Cm-3). During the Station Fire, primary production was a key formation mechanism for WSOC. High concentrations of WSOC (up to 41 μg Cm-3) 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 m/z 44:;m/z 57 and ;m/z 44:;m/z 43, were elevated in those air masses. Intercomparisons of relative amounts of WSOC, organics, ;m/z 44, and m/z 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.

Original languageEnglish (US)
Pages (from-to)8257-8270
Number of pages14
JournalAtmospheric Chemistry and Physics
Volume11
Issue number16
DOIs
StatePublished - 2011

ASJC Scopus subject areas

  • Atmospheric Science

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