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| Titel |
Summertime PM2.5 ionic species in four major cities of China: nitrate formation in an ammonia-deficient atmosphere |
| VerfasserIn |
R. K. Pathak, W. S. Wu, T. Wang |
| 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 ; 9, no. 5 ; Nr. 9, no. 5 (2009-03-06), S.1711-1722 |
| Datensatznummer |
250007007
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| Publikation (Nr.) |
 copernicus.org/acp-9-1711-2009.pdf |
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| Zusammenfassung |
| Strong atmospheric photochemistry in summer can produce a significant amount
of secondary aerosols, which may have a large impact on regional air quality
and visibility. In the study reported herein, we analyzed sulfate, nitrate,
and ammonium in PM2.5 samples collected using a 24-h filter system at
suburban and rural sites near four major cities in China (Beijing, Shanghai,
Guangzhou, and Lanzhou). Overall, the PM2.5 mass concentrations were
high (with a mean value of 55–68 gμgm−3), which reflects
the long-known particulate pollution in China's large urban centers. We
observed very high concentrations of sulfate and nitrate at the Beijing and
Shanghai sites, and, in particular, abnormally high levels of nitrate (24-h
average concentration up to 42 gμgm−3 and contributing up
to 25% of the PM2.5 mass) in the ammonium-poor samples. The Beijing
and Shanghai aerosols were characterized by high levels of aerosol acidity
(~220–390 nmol m−3) and low levels of in-situ pH (−0.77 to −0.52). In
these samples, the formation of the observed high concentrations of
particulate nitrate cannot be explained by homogeneous gas-phase reaction
between ammonia and nitric acid. Examination of the relation of nitrate to
relative humidity and aerosol loading suggests that the nitrate was most
probably formed via the heterogeneous hydrolysis of N2O5 on the
surface of the moist and acidic aerosols in Beijing and Shanghai. In
comparison, the samples collected in Lanzhou and Guangzhou were
ammonium-rich with low levels of aerosol acidity (~65–70 nmol m−3),
and the formation of ammonium nitrate via the homogeneous
gas-phase reaction was favored, which is similar to many previous studies.
An empirical fit has been derived to relate fine nitrate to aerosol acidity,
aerosol water content, aerosol surface area, and the precursor of nitrate
for the data from Beijing and Shanghai. |
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