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| Titel |
Molecular composition of dicarboxylic acids, ketocarboxylic acids, α-dicarbonyls and fatty acids in atmospheric aerosols from Tanzania, East Africa during wet and dry seasons |
| VerfasserIn |
S. L. Mkoma, K. Kawamura |
| 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 ; 13, no. 4 ; Nr. 13, no. 4 (2013-02-26), S.2235-2251 |
| Datensatznummer |
250018434
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| Publikation (Nr.) |
 copernicus.org/acp-13-2235-2013.pdf |
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| Zusammenfassung |
| Atmospheric aerosol samples of PM2.5 and PM10 were collected
during the wet and dry seasons in 2011 from a rural site in Tanzania and
analysed for water-soluble dicarboxylic acids, ketocarboxylic acids,
α-dicarbonyls, and fatty acids using a gas chromatography/flame
ionization detector (GC/FID) and GC/mass spectrometry. Here we report the
molecular composition and sources of diacids and related compounds for wet and
dry seasons. Oxalic acid (C2) was found as the most abundant diacid
species followed by succinic and/or malonic acids whereas glyoxylic acid and
glyoxal were the dominant ketoacid and α-dicarbonyl, respectively in
both seasons in PM2.5 and PM10. Mean concentration of C2 in
PM2.5 (121 ± 47 ng m−3) was lower in wet season than dry season
(258 ± 69 ng m−3). Similarly, PM10 samples showed lower
concentration of C2 (169 ± 42 ng m−3) in wet season than dry season
(292 ± 165 ng m−3). Relative abundances of C2 in total diacids were
65% and 67% in PM2.5 and 65% and 64% in PM10
in the wet and dry seasons, respectively.
Total concentrations of diacids (289–362 ng m−3), ketoacids
(37.8–53.7 ng m−3), and α-dicarbonyls (5.7–7.8 ng m−3)
in Tanzania are higher than those reported at a rural background site in
Nylsvley (South Africa) but comparable or lower than those reported from sites
in Asia and Europe. Diacids and ketoacids were found to be present mainly in
PM2.5 in both seasons (total α-dicarbonyls in the dry
season), suggesting a production of organic acids from pyrogenic sources and
photochemical oxidations. Averaged contributions of total diacids to aerosol
total carbon were 1.4% in PM2.5 and 2.1% in PM10 during wet
season and 3.3% in PM2.5 and 3.9% in PM10 during dry season
whereas those to water-soluble organic carbon were 2.2% and 4.7% in
PM2.5 during wet season and 3.1% and 5.8% in PM10 during dry
season. The higher ratios in dry season suggest an enhanced photochemical
oxidation of organic precursors probably via heterogeneous reactions on
aerosols under strong solar radiation. Strong positive correlations were
found among diacids and related compounds as well as good relations to
source tracers in both seasons, suggesting a mixed source from natural
biogenic emissions, biomass burning, biofuel combustion, and photochemical
production. |
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