Impact of a large wildfire on water-soluble organic aerosol in a major urban area: the 2009 Station Fire in Los Angeles County 1Department of Atmospheric Sciences, University of Arizona, P.O. Box 210081, Tucson, Arizona, 85721, USA
15 Aug 2011
2Departments of Environmental Science and Engineering and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, California 91125, USA
3Department of Chemical and Environmental Engineering, Univ. of Arizona, P.O. Box 210011, Tucson, Arizona, 85721, USA
Received: 13 Apr 2011 – Published in Atmos. Chem. Phys. Discuss.: 27 Apr 2011 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 C m−3). During
the Station Fire, primary production was a key formation mechanism for WSOC.
High concentrations of WSOC (up to 41 μg C m−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.
Revised: 24 Jun 2011 – Accepted: 02 Aug 2011 – Published: 15 Aug 2011
Citation: Wonaschütz, A., Hersey, S. P., Sorooshian, A., Craven, J. S., Metcalf, A. R., Flagan, R. C., and Seinfeld, J. H.: Impact of a large wildfire on water-soluble organic aerosol in a major urban area: the 2009 Station Fire in Los Angeles County, Atmos. Chem. Phys., 11, 8257-8270, doi:10.5194/acp-11-8257-2011, 2011.