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| Titel |
Differences across the ITCZ in the chemical characteristics of the Indian Ocean MBL aerosol during INDOEX |
| VerfasserIn |
M. Norman, C. Leck, H. Rodhe |
| 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 ; 3, no. 3 ; Nr. 3, no. 3 (2003-05-28), S.563-579 |
| Datensatznummer |
250001032
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| Publikation (Nr.) |
 copernicus.org/acp-3-563-2003.pdf |
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| Zusammenfassung |
| The water soluble inorganic part of the sub-micrometer aerosol was measured from two
research vessels over the Indian Ocean during the winter monsoon season (February and
March) as part of the INDOEX project in 1998 and 1999. Additional measurements were
made of gas phase SO2 from one of the vessels in 1999. All samples collected north of the Inter Tropical Convergence Zone,
ITCZ, were clearly affected by continental, anthropogenic sources. A sharp transition
occurred across the ITCZ with concentrations of nss-SO42-,
NH4+ and nss-K+ being lower by a factor of
7-15, >20 and >40, respectively, on the southern side of the ITCZ. The
contribution from DMS to the sub-micrometer nss-SO42- was estimated to be up to
40% in clean air north of the ITCZ but less than 10% in polluted air originating from India. South
of the ITCZ virtually all nss-SO42- was likely to be derived from oxidation of DMS. The
concentration of SO2 decreased rapidly with distance from the Indian coast, the molar ratio
SO2/nss-SO42- reaching values below 5% after
35 h travel time over the ocean. Surprisingly, MSA, which is derived from DMS, also showed higher concentrations in the
sub-micrometer aerosol north of the ITCZ than south of it. This could be explained by the
larger sub-micrometer surface area available north of the ITCZ for the condensation of
MSA. South of the ITCZ a major part of the MSA was found on the super-micrometer
particles. An analysis based on the air trajectories showed that systematic variation in the observed concentrations was associated with variations in the
transport from source regions. For example, differences in time since air parcels left the
Arabian or Indian coasts was shown to be an important factor for explaining the substantial
differences in absolute concentrations. |
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