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| Titel |
Five-year record of atmospheric precipitation chemistry in urban Beijing, China |
| VerfasserIn |
F. Yang, J. Tan, Z. B. Shi, Y. Cai, K. He, Y. Ma, F. Duan, T. Okuda, S. Tanaka, G. Chen |
| 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 ; 12, no. 4 ; Nr. 12, no. 4 (2012-02-21), S.2025-2035 |
| Datensatznummer |
250010738
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| Publikation (Nr.) |
 copernicus.org/acp-12-2025-2012.pdf |
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| Zusammenfassung |
| To investigate the chemical characteristics of precipitation in the polluted
urban atmosphere in Beijing and possible mechanisms influencing their
variations, a total of 131 event-based precipitation samples were collected
from March 2001 to August 2005. The concentrations of major ions in the
samples were analyzed by using ion chromatography. Intermediate pH (6.1–7.3)
was recorded in approximately two-thirds of the precipitation samples and
acidic pH (4.2–5.6) in only 16% of the samples. However, the
precipitation acidity was on the growth track and the process was likely
being accelerated. SO42−, NO3−, NH4+, and
Ca2+ were the most abundant ions in the precipitations, with their
single volume-weighted mean (VWM) concentration all above 100 μeq l−1. The two major anions and two major cations accounted for more than
80% of total anionic and cationic mass, respectively. The VWM
SO42− concentration decreased by 13% compared to that during
1995–1998, much less than the 58% reduction in the annual average
SO2 concentration from 1998 to 2005 in Beijing. What seems more
counterintuitive is that the VWM NO3− concentration nearly doubled
over the period although the annual average NO2 concentration decreased
by 5% from 1998 to 2005. These results imply that the conversion of
gaseous precursors to acid compounds and/or the regional transport were
reinforced over the decade. The average ratio of neutralizing potential to
acidifying potential (i.e. NP/AP) was as high as 1.2 but experienced an
evident decline trend. This was mainly ascribed to reduced input of
NH4+ and Ca2+ and increased input of NO3−.
Furthermore, the equivalent mass ratio of NO3− to non-sea-salt
SO42− presented an increasing trend over the study period,
suggesting that the contribution of NO3− to the precipitation
acidity increased in recent years. However, the mean ratio was only
0.37 ± 0.11 in the study period, which is significantly lower than those reported
in some metropolitan areas in developed countries. This shows that the
precipitation acidity in Beijing was still dominantly from SO2 while the SO2 contribution was progressively substituted by NOx. |
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