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| Titel |
Seasonal differences in the vertical profiles of aerosol optical properties over rural Oklahoma |
| VerfasserIn |
E. Andrews, P. J. Sheridan, J. A. Ogren |
| 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 ; 11, no. 20 ; Nr. 11, no. 20 (2011-10-27), S.10661-10676 |
| Datensatznummer |
250010150
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| Publikation (Nr.) |
 copernicus.org/acp-11-10661-2011.pdf |
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| Zusammenfassung |
| A small airplane made 597 aerosol optical property (light
absorption and light scattering) vertical profile measurements over a rural
Oklahoma site between March 2000 and December 2007. The aerosol profiles
obtained during these 8 yr of measurements suggest significant seasonal
differences in aerosol loading (scattering and absorption). The highest
amounts of scattering and absorbing aerosol are observed during the summer
and the lowest loading occurs during the winter. The relative contribution
of aerosol absorption is highest in the winter (i.e., single scattering
albedo is lowest in winter), particularly aloft. Aerosol absorption
generally decreased with altitude below ~1.5 km and then was
relatively constant or decreased more gradually above that. Aerosol
scattering decreased sharply with altitude below ~1.5 km but, unlike
absorption, also decreased at higher altitudes, albeit less sharply.
Scattering Ångström exponents suggest that the aerosol was dominated
by sub-micron aerosol during the summer at all altitudes, but that larger
particles were present, especially in the spring and winter above 1 km. The
seasonal variability observed for aerosol loading is consistent with AERONET
aerosol optical depth (AOD) although the AOD values calculated from in situ
adjusted to ambient conditions and matching wavelengths are up to a factor
of two lower than AERONET AOD values depending on season. The column
averaged single scattering albedo derived from in situ airplane measurements
are similar in value to the AERONET single scattering albedo inversion
product but the seasonal patterns are different – possibly a consequence of
the strict constraints on obtaining single scattering albedo from AERONET
data. A comparison of extinction Ångström exponent and asymmetry
parameter from the airplane and AERONET platforms suggests similar seasonal
variability with smaller particles observed in the summer and fall and
larger particles observed in spring and winter. The observed seasonal cycle
of aerosol loading corresponds with changes in air mass back trajectories:
the aerosol scattering was higher when transport was from polluted areas
(e.g., the Gulf Coast) and lower when the air came from cleaner regions
and/or the upper atmosphere. |
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