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| Titel |
The contribution of oceanic methyl iodide to stratospheric iodine |
| VerfasserIn |
S. Tegtmeier, K. Krüger, B. Quack, E. Atlas, D. R. Blake, H. Boenisch, A. Engel, H. Hepach, R. Hossaini, M. A. Navarro, S. Raimund, S. Sala, Q. Shi, F. Ziska |
| 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. 23 ; Nr. 13, no. 23 (2013-12-09), S.11869-11886 |
| Datensatznummer |
250085861
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| Publikation (Nr.) |
 copernicus.org/acp-13-11869-2013.pdf |
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| Zusammenfassung |
| We investigate the contribution of oceanic methyl iodide (CH3I) to the
stratospheric iodine budget. Based on CH3I measurements from three
tropical ship campaigns and the Lagrangian transport model FLEXPART, we
provide a detailed analysis of CH3I transport from the ocean surface to
the cold point in the upper tropical tropopause layer (TTL). While average
oceanic emissions differ by less than 50% from campaign to campaign, the
measurements show much stronger variations within each campaign. A positive
correlation between the oceanic CH3I emissions and the efficiency of
CH3I troposphere–stratosphere transport has been identified for some
cruise sections. The mechanism of strong horizontal surface winds triggering
large emissions on the one hand and being associated with tropical
convective systems, such as developing typhoons, on the other hand, could
explain the identified correlations. As a result of the simultaneous
occurrence of large CH3I emissions and strong vertical uplift,
localized maximum mixing ratios of 0.6 ppt CH3I at the cold point have
been determined for observed peak emissions during the SHIVA (Stratospheric Ozone:
Halogen Impacts in a Varying Atmosphere)-Sonne research vessel campaign
in the coastal western Pacific. The other two campaigns give considerably
smaller maxima of 0.1 ppt CH3I in the open
western Pacific and 0.03 ppt in the coastal eastern Atlantic. In order to assess the representativeness of the
large local mixing ratios, we use climatological emission scenarios to derive
global upper air estimates of CH3I abundances. The model results are
compared with available upper air measurements, including data from the
recent ATTREX and HIPPO2 aircraft campaigns. In the eastern Pacific region, the
location of the available measurement campaigns in the upper TTL, the
comparisons give a good agreement, indicating that around 0.01 to 0.02 ppt of
CH3I enter the stratosphere. However, other tropical regions that are
subject to stronger convective activity show larger CH3I entrainment,
e.g., 0.08 ppt in the western Pacific. Overall our model results give a
tropical contribution of 0.04 ppt CH3I to the stratospheric iodine
budget. The strong variations in the geographical distribution of CH3I
entrainment suggest that currently available upper air measurements are not
representative of global estimates and further campaigns will be necessary
in order to better understand the CH3I contribution to stratospheric
iodine. |
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