 |
| Titel |
Water-Soluble Organic Aerosol material and the light-absorption characteristics of aqueous extracts measured over the Southeastern United States |
| VerfasserIn |
A. Hecobian, X. Zhang, M. Zheng, N. Frank, E. S. Edgerton, R. J. Weber |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 13 ; Nr. 10, no. 13 (2010-07-02), S.5965-5977 |
| Datensatznummer |
250008595
|
| Publikation (Nr.) |
 copernicus.org/acp-10-5965-2010.pdf |
|
|
|
|
|
| Zusammenfassung |
| Light absorption of fine particle (PM2.5) aqueous extracts between
wavelengths of 200 and 800 nm were investigated from two data sets: 24-h
Federal Reference Method (FRM) filter extracts from 15 Southeastern US
monitoring sites over the year of 2007 (900 filters), and online
measurements from a Particle-Into-Liquid Sampler deployed from July to
mid-August 2009 in Atlanta, Georgia. Three main sources of soluble
chromophores were identified: biomass burning, mobile source emissions, and
compounds linked to secondary organic aerosol (SOA) formation. Absorption
spectra of aerosol solutions from filter extracts were similar for different
sources. Angstrom exponents were ~7±1 for biomass burning and
non-biomass burning-impacted 24-h filter samples (delineated by a
levoglucosan concentration of 50 ng m−3) at both rural and urban sites.
The absorption coefficient from measurements averaged between wavelength 360
and 370 nm (Abs365, in units m−1) was used as a measure of overall
brown carbon light absorption. Biomass-burning-impacted samples were highest
during winter months and Abs365 was correlated with levoglucosan at all
sites. During periods of little biomass burning in summer, light absorbing
compounds were still ubiquitous and correlated with fine particle
Water-Soluble Organic Carbon (WSOC), but comprised a much smaller fraction
of the WSOC, where Abs365/WSOC (i.e., mass absorption efficiency) was
typically ~3 times higher in biomass burning-impacted samples. Factor
analysis attributed 50% of the yearly average Abs365 to biomass burning
sources. Brown carbon from primary urban emissions (mobile sources) was also
observed and accounted for ~10% of the regional yearly average
Abs365. Summertime diurnal profiles of Abs365 and WSOC showed that
morning to midday increases in WSOC from photochemical production were
associated with a decrease in Abs365/WSOC. After noon, this ratio
substantially increased, indicating that either some fraction of the
non-light absorbing fresh SOA was rapidly (within hours) converted to
chromophores heterogeneously, or that SOA from gas-particle partitioning
later in the day was more light-absorbing. Factor analysis on the 24-h
integrated filter data associated ~20 to 30% of Abs365 over 2007
with a secondary source that was highest in summer and also the main source
for oxalate, suggesting that aqueous phase reactions may account for the
light-absorbing fraction of WSOC observed throughout the Southeastern US
in summer. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|