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  Methyl chloride in the upper troposphere observed by the CARIBIC passenger aircraft observatory: Large-scale distributions and Asian summer monsoon outflow

Umezawa, T., Baker, A. K., Oram, D., Sauvage, C., O'Sullivan, D., Rauthe-Schöch, A., et al. (2014). Methyl chloride in the upper troposphere observed by the CARIBIC passenger aircraft observatory: Large-scale distributions and Asian summer monsoon outflow. Journal of Geophysical Research-Atmospheres, 119(9), 5542-5558. doi:10.1002/2013JD021396.

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Umezawa, T.1, Author              
Baker, A. K.1, Author              
Oram, D.2, Author
Sauvage, C.1, Author              
O'Sullivan, D.2, Author
Rauthe-Schöch, A.1, Author              
Montzka, S. A.2, Author
Zahn, A.2, Author
Brenninkmeijer, C. A. M.1, Author              
Affiliations:
1Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society, ou_1826285              
2external, ou_persistent22              

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 Abstract: We present spatial and temporal variations of methyl chloride (CH3Cl) in the upper troposphere (UT) observed mainly by the Civil Aircraft for Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) passenger aircraft for the years 2005-2011. The CH3Cl mixing ratio in the UT over Europe was higher than that observed at a European surface baseline station throughout the year, indicative of a persistent positive vertical gradient at Northern Hemisphere midlatitudes. A series of flights over Africa and South Asia show that CH3Cl mixing ratios increase toward tropical latitudes, and the observed UT CH3Cl level over these two regions and the Atlantic was higher than that measured at remote surface sites. Strong emissions of CH3Cl in the tropics combined with meridional air transport through the UT may explain such vertical and latitudinal gradients. Comparisons with carbon monoxide (CO) data indicate that noncombustion sources in the tropics dominantly contribute to forming the latitudinal gradient of CH3Cl in the UT. We also observed elevated mixing ratios of CH3Cl and CO in air influenced by biomass burning in South America and Africa, and the enhancement ratios derived for CH3Cl to CO in those regions agree with previous observations. In contrast, correlations indicate a high CH3Cl to CO ratio of 2.9 +/- 0.5 ppt ppb(-1) in the Asian summer monsoon anticyclone and domestic biofuel emissions in South Asia are inferred to be responsible. We estimated the CH3Cl emission in South Asia to be 134 +/- 23 Gg Cl yr(-1), which is higher than a previous estimate due to the higher CH3Cl to CO ratio observed in this study.

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 Dates: 2014
 Publication Status: Published in print
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 Rev. Type: -
 Identifiers: ISI: 000338340400034
DOI: 10.1002/2013JD021396
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Title: Journal of Geophysical Research-Atmospheres
Source Genre: Journal
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Publ. Info: Washington, D.C. : American Geophysical Union
Pages: - Volume / Issue: 119 (9) Sequence Number: - Start / End Page: 5542 - 5558 Identifier: ISSN: 0148-0227
CoNE: https://pure.mpg.de/cone/journals/resource/991042728714264_1