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| Titel |
Assessment of long-term WRF–CMAQ simulations for understanding direct aerosol effects on radiation "brightening" in the United States |
| VerfasserIn |
C.-M. Gan, J. Pleim, R. Mathur, C. Hogrefe, C. N. Long, J. Xing, D. Wong, R. Gilliam, 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 ; 15, no. 21 ; Nr. 15, no. 21 (2015-11-03), S.12193-12209 |
| Datensatznummer |
250120138
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| Publikation (Nr.) |
 copernicus.org/acp-15-12193-2015.pdf |
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| Zusammenfassung |
| Long-term simulations with the coupled WRF–CMAQ (Weather Research
and Forecasting–Community Multi-scale Air Quality) model have been conducted to
systematically investigate the changes in anthropogenic emissions of SO2
and NOx over the past 16 years (1995–2010) across the United States
(US), their impacts on anthropogenic aerosol loading over North America, and
subsequent impacts on regional radiation budgets. In particular, this study
attempts to determine the consequences of the changes in tropospheric aerosol
burden arising from substantial reductions in emissions of SO2 and
NOx associated with control measures under the Clean Air Act (CAA)
especially on trends in solar radiation. Extensive analyses conducted by Gan
et al. (2014a) utilizing observations (e.g., SURFRAD, CASTNET, IMPROVE, and
ARM) over the past 16 years (1995–2010) indicate a shortwave (SW) radiation
(both all-sky and clear-sky) "brightening" in the US. The relationship of
the radiation brightening trend with decreases in the aerosol burden is less
apparent in the western US. One of the main reasons for this is that the
emission controls under the CAA were aimed primarily at reducing pollutants
in areas violating national air quality standards, most of which were located
in the eastern US, while the relatively less populated areas in the western US
were less polluted at the beginning of this study period. Comparisons of
model results with observations of aerosol optical depth (AOD), aerosol
concentration, and radiation demonstrate that the coupled WRF–CMAQ model is
capable of replicating the trends well even though it tends to underestimate
the AOD. In particular, the sulfate concentration predictions were well
matched with the observations. The discrepancies found in the clear-sky
diffuse SW radiation are likely due to several factors such as the potential
increase of ice particles associated with increasing air traffic, the
definition of "clear-sky" in the radiation retrieval methodology, and
aerosol semi-direct and/or indirect effects which cannot be readily isolated
from the observed data. |
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