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| Titel |
Evidence for widespread tropospheric Cl chemistry in free tropospheric air masses from the South China Sea |
| VerfasserIn |
Angela K. Baker, Carina Sauvage, Ute R. Thorenz, Carl A. M. Brenninkmeijer, David E. Oram, Peter van Velthoven, Andreas Zahn, Jonathan Williams |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250110376
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| Publikation (Nr.) |
 EGU/EGU2015-10370.pdf |
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| Zusammenfassung |
| While the primary global atmospheric oxidant is the hydroxyl radical (OH), under
certain circumstances chlorine radicals (Cl) can compete with OH and perturb the
oxidative cycles of the troposphere. During flights between Bangkok, Thailand
and Kuala Lumpur, Malaysia conducted over two fall/winter seasons (November
2012 – March 2013 and November 2013 – January 2014) the IAGOS-CARIBIC
(www.caribic-atmospheric.com) observatory consistently encountered free tropospheric air
masses (9-11 km) originating over the South China Sea which had non-methane
hydrocarbon (NMHC) signatures characteristic of processing by Cl. These signatures were
observed in November and December of both years, but were not seen in other months,
suggesting that oxidation by Cl is a persistent seasonal feature in this region. These
Cl signatures were observed over a range of ~1500 km indicating a large-scale
phenomenon.
In this region, where transport patterns facilitate global redistribution of pollutants and
persistent deep convection creates a fast-track for cross-tropopause transport, there exists the
potential for regional chemistry to have impacts further afield. Here we use observed
relationships between NMHCs to estimate the significance and magnitude of Cl oxidation in
this region. From the relative depletions of NMHCs in these air masses we infer OH to Cl
ratios of 83±28 to 139±40 [OH]/[Cl], which we believe represents an upper limit, based on
the technique employed. At a predicted average [OH] of 1.5x106 OH cm-3 this corresponds
to an average (minimum) [Cl] exposure of 1-2x104 Cl cm-3 during air mass transport.
Lastly, in addition to estimating Cl abundances we have used IAGOS-CARIBIC observations
to elucidate whether the origin of this Cl is predominantly natural or anthropogenic. |
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