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| Titel |
Impact of dust on tropospheric chemistry over polluted regions: a case study of the Beijing megacity |
| VerfasserIn |
S. Zhu, T. Butler, R. Sander, J. Ma, M. G. Lawrence |
| 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. 8 ; Nr. 10, no. 8 (2010-04-26), S.3855-3873 |
| Datensatznummer |
250008377
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| Publikation (Nr.) |
 copernicus.org/acp-10-3855-2010.pdf |
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| Zusammenfassung |
| The box model MECCA (Module Efficiently Calculating the Chemistry of the
Atmosphere) is extended by incorporating detailed heterogeneous chemistry
occurring on mineral aerosol surfaces. The model is used to investigate the
impact of dust on tropospheric photochemistry, when the dust is transported
to a polluted region, focusing on the example of Beijing. The impacts of
dust via heterogeneous removal of gases are analyzed for different
hypothetical transport rates, which are described by four different exchange
rate coefficients Kt in the model. Along with the dust, airmasses with
trace gas levels characteristic for regions upwind of Beijing are
transported with the same rate (Kt). Substantial impacts are found for
many gases, including Ox (O3+O(3P)), NOx (NO+NO2)
and OH. The Ox daily average mixing ratio decreases due to
heterogeneous reactions on dust. The change ranges from −2.5 to
−18.4 nmol mol−1, and is larger for faster mixing with upwind air masses
(i.e. greater Kt). This translates into a large relative change in Ox,
ranging from −44% to −55%, depending on Kt. By assuming an
artificial 50% decrease of all photolysis rates, the impacts of dust via
perturbation of the photolysis rates in the polluted region are also
estimated. Furthermore, the uncertainties in the results due to the
uncertainties in the uptake coefficients are evaluated. It is found that for
all gases which are heterogeneously removed, the self-removal results in the
largest uncertainty (e.g. −49% for O3, −76% for NO2, −47%
for HNO3, −92% for HCHO, −64% for CH3OH and −93% for
SO2). The heterogeneous removal of NO2 is found to be particularly
important, because it results in significant levels of uncertainty not only
for itself, but also for OH (340%) and HO2 (365%). Moreover, the
heterogeneous removal rates of HCHO and O3 also have farther-reaching
effects on the OH concentration (resulting in changes of −55% and 45%,
respectively), and the heterogeneous removal of HCHO results in an
uncertainty of −38% in the HO2 concentration. The limitations of
MECCA due to its missing oxidation mechanism for aromatics and other higher
VOC species has also been considered, and shown to be potentially important
in the quantitative results, though not likely to change the qualitative
results of this study. |
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