Source apportionment and seasonal variation of PM<sub>2.5</sub> in a Sub-Saharan African city: Nairobi, Kenya
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, PM<sub>2.5</sub>) we...
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doaj-8f5fb77c3e014bf7ae25d735a81824ac2020-11-25T00:59:47ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242014-09-0114189977999110.5194/acp-14-9977-2014Source apportionment and seasonal variation of PM<sub>2.5</sub> in a Sub-Saharan African city: Nairobi, KenyaS. M. Gaita0J. Boman1M. J. Gatari2J. B. C. Pettersson3S. Janhäll4Department of Chemistry and Molecular Biology, Atmospheric Science, University of Gothenburg, 412 96 Gothenburg, SwedenDepartment of Chemistry and Molecular Biology, Atmospheric Science, University of Gothenburg, 412 96 Gothenburg, SwedenInstitute of Nuclear Science and Technology, University of Nairobi, P.O. Box 30197, 00100 Nairobi, KenyaDepartment of Chemistry and Molecular Biology, Atmospheric Science, University of Gothenburg, 412 96 Gothenburg, SwedenVTI – Swedish National Road and Transport Research Institute, P.O. Box 8072, 402 78 Gothenburg, SwedenSources 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, PM<sub>2.5</sub>) 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 PM<sub>2.5</sub> concentration at the urban background site was 21±9.5 μg m<sup>−3</sup>, whereas the concentration at the suburban site was 13±7.3 μg m<sup>−3</sup>. The daily PM<sub>2.5</sub> concentrations exceeded 25 μg m<sup>−3</sup> (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 PM<sub>2.5</sub> 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 PM<sub>2.5</sub>. 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.http://www.atmos-chem-phys.net/14/9977/2014/acp-14-9977-2014.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
S. M. Gaita J. Boman M. J. Gatari J. B. C. Pettersson S. Janhäll |
spellingShingle |
S. M. Gaita J. Boman M. J. Gatari J. B. C. Pettersson S. Janhäll Source apportionment and seasonal variation of PM<sub>2.5</sub> in a Sub-Saharan African city: Nairobi, Kenya Atmospheric Chemistry and Physics |
author_facet |
S. M. Gaita J. Boman M. J. Gatari J. B. C. Pettersson S. Janhäll |
author_sort |
S. M. Gaita |
title |
Source apportionment and seasonal variation of PM<sub>2.5</sub> in a Sub-Saharan African city: Nairobi, Kenya |
title_short |
Source apportionment and seasonal variation of PM<sub>2.5</sub> in a Sub-Saharan African city: Nairobi, Kenya |
title_full |
Source apportionment and seasonal variation of PM<sub>2.5</sub> in a Sub-Saharan African city: Nairobi, Kenya |
title_fullStr |
Source apportionment and seasonal variation of PM<sub>2.5</sub> in a Sub-Saharan African city: Nairobi, Kenya |
title_full_unstemmed |
Source apportionment and seasonal variation of PM<sub>2.5</sub> in a Sub-Saharan African city: Nairobi, Kenya |
title_sort |
source apportionment and seasonal variation of pm<sub>2.5</sub> in a sub-saharan african city: nairobi, kenya |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2014-09-01 |
description |
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, PM<sub>2.5</sub>) 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 PM<sub>2.5</sub> concentration at the urban
background site was 21±9.5 μg m<sup>−3</sup>, whereas the
concentration at the suburban site was 13±7.3 μg m<sup>−3</sup>.
The daily PM<sub>2.5</sub> concentrations exceeded 25 μg m<sup>−3</sup> (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 PM<sub>2.5</sub> 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 PM<sub>2.5</sub>.
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. |
url |
http://www.atmos-chem-phys.net/14/9977/2014/acp-14-9977-2014.pdf |
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