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Titel |
Source apportionment and seasonal variation of PM2.5 in a Sub-Saharan African city: Nairobi, Kenya |
VerfasserIn |
S. M. Gaita, J. Boman, M. J. Gatari, J. B. C. Pettersson, S. Janhäll |
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 ; 14, no. 18 ; Nr. 14, no. 18 (2014-09-19), S.9977-9991 |
Datensatznummer |
250119053
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Publikation (Nr.) |
copernicus.org/acp-14-9977-2014.pdf |
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Zusammenfassung |
Sources of airborne particulate matter and their seasonal variation in urban
areas in Sub-Saharan Africa are poorly understood due to lack of long-term
measurement data. In view of this, filter samples of airborne particulate
matter (particle diameter ≤2.5 μm, PM2.5) were collected
between May 2008 and April 2010 at two sites (urban background site and
suburban site) within the Nairobi metropolitan area. A total of 780 samples
were collected and analyzed for particulate mass, black carbon (BC) and
13 trace elements. The average PM2.5 concentration at the urban
background site was 21±9.5 μg m−3, whereas the
concentration at the suburban site was 13±7.3 μg m−3.
The daily PM2.5 concentrations exceeded 25 μg m−3 (the
World Health Organization 24 h guideline value) on 29% of the days at the
urban background site and 7% of the days at the suburban site. At both
sites, BC, Fe, S and Cl accounted for approximately 80% of all detected
elements. Positive matrix factorization analysis identified five source
factors that contribute to PM2.5 in Nairobi, namely traffic, mineral
dust, industry, combustion and a mixed factor (composed of biomass
burning, secondary aerosol and aged sea salt). Mineral dust and traffic
factors were related to approximately 74% of PM2.5.
The identified source factors exhibited seasonal variation, apart from
the traffic factor, which was prominently consistent throughout the sampling
period. Weekly variations
were observed in all factors, with weekdays having higher concentrations than
weekends. The results provide information that can be exploited for policy
formulation and mitigation strategies to control air pollution in Sub-Saharan
African cities. |
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