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| Titel |
A multi-year study of lower tropospheric aerosol variability and systematic relationships from four North American regions |
| VerfasserIn |
J. P. Sherman, P. J. Sheridan, J. A. Ogren, E. Andrews, D. Hageman, L. Schmeisser, A. Jefferson, S. Sharma |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 21 ; Nr. 15, no. 21 (2015-11-10), S.12487-12517 |
| Datensatznummer |
250120153
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| Publikation (Nr.) |
 copernicus.org/acp-15-12487-2015.pdf |
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| Zusammenfassung |
Hourly averaged aerosol optical properties (AOPs) measured over the years
2010–2013 at four continental North American NOAA Earth System Research
Laboratory (NOAA/ESRL) cooperative aerosol network sites – Southern Great
Plains near Lamont, OK (SGP), Bondville, IL (BND), Appalachian State
University in Boone, NC (APP), and Egbert, Ontario, Canada (EGB) are
analyzed. Aerosol optical properties measured over 1996–2009 at BND and
1997–2009 at SGP are also presented. The aerosol sources and types in the
four regions differ enough so as to collectively represent rural,
anthropogenically perturbed air conditions over much of eastern continental
North America. Temporal AOP variability on monthly, weekly, and diurnal
timescales is presented for each site. Differences in annually averaged AOPs
and those for individual months at the four sites are used to examine
regional AOP variability. Temporal and regional variability are placed in
the context of reported aerosol chemistry at the sites, meteorological
measurements (wind direction, temperature), and reported regional mixing
layer heights. Basic trend analysis is conducted for selected AOPs at the
long-term sites (BND and SGP). Systematic relationships among AOPs are also
presented.
Seasonal variability in PM1 (sub-1 μm particulate matter) scattering and
absorption coefficients at 550 nm (σsp and σap,
respectively) and most of the other PM1 AOPs is much larger than day of week
and diurnal variability at all sites. All sites demonstrate summer σsp and σap peaks. Scattering coefficient decreases by a
factor of 2–4 in September–October and coincides with minimum
single-scattering albedo (ω0) and maximum hemispheric
backscatter fraction (b). The co-variation of ω0 and b lead to
insignificant annual cycles in top-of-atmosphere direct radiative forcing
efficiency (DRFE) at APP and SGP. Much larger annual DRFE cycle amplitudes
are observed at EGB (~ 40 %) and BND (~ 25 %), with least negative DRFE in September–October at both sites.
Secondary winter peaks in σsp are observed at all sites except
APP. Amplitudes of diurnal and weekly cycles in σap at the
sites are larger for all seasons than those of σsp, with
the largest differences occurring in summer. The weekly and diurnal cycle
amplitudes of most intensive AOPs (e.g., those derived from ratios of
measured σsp and σap) are minimal in most cases,
especially those related to parameterizations of aerosol size distribution.
Statistically significant trends in σsp (decreasing), PM1
scattering fraction (decreasing), and b (increasing) are found at BND from
1996 to 2013 and at SGP from 1997 to 2013. A statistically significant decreasing
trend in PM10 scattering Ångström exponent is also observed for SGP
but not BND. Most systematic relationships among AOPs are similar for the
four sites and are adequately described for individual seasons by
annually averaged relationships, although relationships involving absorption
Ångström exponent vary with site and season. |
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