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| Titel |
Assessment of the effect of air pollution controls on trends in shortwave radiation over the United States from 1995 through 2010 from multiple observation networks |
| VerfasserIn |
C.-M. Gan, J. Pleim, R. Mathur, C. Hogrefe, C. N. Long, J. Xing, S. Roselle, C. Wei |
| 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 ; 14, no. 3 ; Nr. 14, no. 3 (2014-02-14), S.1701-1715 |
| Datensatznummer |
250118377
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| Publikation (Nr.) |
 copernicus.org/acp-14-1701-2014.pdf |
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| Zusammenfassung |
| Long-term data sets of all-sky and clear-sky downwelling shortwave (SW)
radiation, cloud cover fraction, and aerosol optical depth (AOD) were
analyzed together with surface concentrations from several networks (e.g.,
Surface Radiation Budget Network (SURFRAD), Clean Air Status and Trend
Network (CASTNET), Interagency Monitoring of Protection Visual Environments
(IMPROVE) and Atmospheric Radiation Measurement (ARM)) in the United States
(US). Seven states with varying climatology were selected to better
understand the effects of aerosols and clouds on SW radiation. This analysis
aims to assess the effects of reductions in anthropogenic aerosol burden
resulting from substantial reductions in emissions of sulfur dioxide
(SO2) and nitrogen oxides (NOx) over the past 16 yr across
the US, based on trends in SW radiation. The SO2 and NOx
emission data show decreasing trends from 1995 to 2010, which indirectly
validates the effects of the Clean Air Act (CAA) in the US. Meanwhile, the
total column AOD and surface total PM2.5 observations also show
decreasing trends in the eastern US but slightly increasing trends in the
western US. Moreover, measured surface concentrations of several other
pollutants (i.e., SO2, SO4 and NOx) have similar
behavior to AOD and total PM2.5. Analysis of the observed data shows
strong increasing trends in all-sky downwelling SW radiation with decreasing
trends in cloud cover. However, since observations of both all-sky direct and
diffuse SW radiation show increasing trends, there may be other factors
contributing to the radiation trends in addition to the decreasing trends in
overall cloud cover. To investigate the role of direct radiative effects of
aerosols, clear-sky downwelling radiation is analyzed so that cloud effects
are eliminated. However, similar increasing trends in clear-sky total and
diffuse SW radiation are observed. While significantly decreasing trends in
AOD and surface PM2.5 concentrations along with increasing SW radiation
(both all-sky and clear-sky) in the eastern US during 1995–2010 imply the
occurrence of direct aerosol mediated "brightening", the increasing trends
of both all-sky and clear-sky diffuse SW radiation contradicts this
conclusion since diffuse radiation would be expected to decrease as aerosols
direct effects decrease and cloud cover decreases. After investigating
several confounding factors, the increasing trend in clear-sky diffuse SW may
be due to more high-level cirrus from increasing air traffic over the US. The
clear-sky radiation observations in the western US also show indications of
"brightening" even though the AOD, PM2.5 and surface concentration do
not vary drastically. This outcome was not unexpected because the CAA
controls were mainly aimed at reducing air pollutant emissions in the eastern
US and air pollutant levels in the western US were much lower at the onset.
This suggests other factors affect the "brightening" especially in the
western US. |
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