Journal article

Spatial and seasonal variations of fine particle water-soluble organic carbon (WSOC) over the southeastern United States: Implications for secondary organic aerosol formation

Zhang X, Liu Z, Hecobian A, Zheng M, Frank N, Edgerton E, Weber R ...see all

Atmospheric Chemistry and Physics, vol. 12, issue 14 (2012) pp. 6593-6607

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Abstract

Secondary organic aerosol (SOA) in the southeastern US is investigated
by analyzing the spatial-temporal distribution of water-soluble organic
carbon (WSOC) and other PM2.5 components from 900 archived 24-h Teflon
filters collected at 15 urban or rural EPA Federal Reference Method
(FRM) network sites throughout 2007. Online measurements of WSOC at an
urban/rural-paired site in Georgia in the summer of 2008 are contrasted
to the filter data. Based on FRM filters, excluding biomass-burning
events (levoglucosan < 50 ng m(-3)), WSOC and sulfate were highly
correlated with PM2.5 mass (r(2)similar to 0.7). Both components
comprised a large mass fraction of PM2.5 (13% and 31%, respectively,
or similar to 25% and 50% for WSOM and ammonium sulfate). Sulfate and
WSOC both tracked ambient temperature throughout the year, suggesting
the temperature effects were mainly linked to faster photochemistry
and/or synoptic meteorology and less due to enhanced biogenic
hydrocarbon emissions. FRM WSOC, and to a lesser extent sulfate, were
spatially homogeneous throughout the region, yet WSOC was moderately
enhanced (27%) in locations of greater predicted isoprene emissions in
summer. A Positive Matrix Factorization (PMF) analysis identified two
major source types for the summer WSOC; 22% of the WSOC were associated
with ammonium sulfate, and 56% of the WSOC were associated with brown
carbon and oxalate. A small urban excess of FRM WSOC (10%) was observed
in the summer of 2007, however, comparisons of online WSOC measurements
at one urban/rural pair (Atlanta/Yorkville) in August 2008 showed
substantially greater difference in WSOC (31%) relative to the FRM
data, suggesting a low bias for urban filters. The measured Atlanta
urban excess, combined with the estimated boundary layer heights, gave
an estimated Atlanta daily WSOC production rate in August of 0.55 mgC
m(-2) h(-1) between mid-morning and mid-afternoon. This study
characterizes the regional nature of fine particles in the southeastern
US, confirming the importance of SOA and the roles of both biogenic and
anthropogenic emissions.

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Authors

  • X. Zhang

  • Z. Liu

  • A. Hecobian

  • M. Zheng

  • N. H. Frank

  • E. S. Edgerton

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