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| Titel |
Enhancement of the aerosol direct radiative effect by semi-volatile aerosol components: airborne measurements in North-Western Europe |
| VerfasserIn |
W. T. Morgan, J. D. Allan, K. N. Bower, M. Esselborn, B. Harris, J. S. Henzing, E. J. Highwood, A. Kiendler-Scharr, G. R. McMeeking, A. A. Mensah, M. J. Northway, S. Osborne, P. I. Williams, R. Krejci, H. Coe |
| 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 ; 10, no. 17 ; Nr. 10, no. 17 (2010-09-01), S.8151-8171 |
| Datensatznummer |
250008742
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| Publikation (Nr.) |
 copernicus.org/acp-10-8151-2010.pdf |
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| Zusammenfassung |
A case study of atmospheric aerosol measurements exploring the impact of the
vertical distribution of aerosol chemical composition upon the radiative
budget in North-Western Europe is presented. Sub-micron aerosol chemical
composition was measured by an Aerodyne Aerosol Mass Spectrometer (AMS) on
both an airborne platform and a ground-based site at Cabauw in the
Netherlands. The examined period in May 2008 was characterised by enhanced
pollution loadings in North-Western Europe and was dominated by ammonium
nitrate and Organic Matter (OM). Both ammonium nitrate and OM were observed
to increase with altitude in the atmospheric boundary layer. This is
primarily attributed to partitioning of semi-volatile gas phase species to
the particle phase at reduced temperature and enhanced relative humidity.
Increased ammonium nitrate concentrations in particular were found to
strongly increase the ambient scattering potential of the aerosol burden,
which was a consequence of the large amount of associated water as well as
the enhanced mass. During particularly polluted conditions, increases in
aerosol optical depth of 50–100% were estimated to occur due to the observed
increase in secondary aerosol mass and associated water uptake. Furthermore,
the single scattering albedo was also shown to increase with height in the
boundary layer. These enhancements combined to increase the negative direct
aerosol radiative forcing by close to a factor of two at the median
percentile level. Such increases have major ramifications for regional
climate predictions as semi-volatile components are often not included in
aerosol models.
The results presented here provide an ideal opportunity to test regional and
global representations of both the aerosol vertical distribution and
subsequent impacts in North-Western Europe. North-Western Europe can be
viewed as an analogue for the possible future air quality over other polluted
regions of the Northern Hemisphere, where substantial reductions in sulphur
dioxide emissions have yet to occur. Anticipated reductions in sulphur
dioxide in polluted regions will result in an increase in the availability of
ammonia to form ammonium nitrate as opposed to ammonium sulphate. This will
be most important where intensive agricultural practises occur. Our
observations over North-Western Europe, a region where sulphur dioxide
emissions have already been reduced, indicate that failure to include the
semi-volatile behaviour of ammonium nitrate will result in significant errors
in predicted aerosol direct radiative forcing. Such errors will be
particularly significant on regional scales. |
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