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Active and Widespread Halogen Chemistry in the Tropical and Subtropical Free TroposphereHalogens in the troposphere are increasingly recognized as playing an important role for atmospheric chemistry, and possibly climate. Bromine and iodine react catalytically to destroy ozone (O3), oxidize mercury, and modify oxidative capacity that is relevant for the lifetime of greenhouse gases. Most of the tropospheric O3 and methane (CH4) loss occurs at tropical latitudes. Here we report simultaneous measurements of vertical profiles of bromine oxide (BrO) and iodine oxide (IO) in the tropical and subtropical free troposphere (10degN to 40degS), and show that these halogens are responsible for 34% of the column-integrated loss of tropospheric O3. The observed BrO concentrations increase strongly with altitude (approx.3.4 pptv at 13.5 km), and are 2-4 times higher than predicted in the tropical free troposphere. BrO resembles model predictions more closely in stratospheric air. The largest model low bias is observed in the lower tropical transition layer (TTL) over the tropical eastern Pacific Ocean, and may reflect a missing inorganic bromine source supplying an additional 2.5-6.4 pptv total inorganic bromine (Bry), or model overestimated Bry wet scavenging. Our results highlight the importance of heterogeneous chemistry on ice clouds, and imply an additional Bry source from the debromination of sea salt residue in the lower TTL. The observed levels of bromine oxidize mercury up to 3.5 times faster than models predict, possibly increasing mercury deposition to the ocean. The halogen-catalyzed loss of tropospheric O3 needs to be considered when estimating past and future ozone radiative effects.
Document ID
20160010796
Acquisition Source
Langley Research Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Wang, Siyuan
(Colorado Univ. Boulder, CO, United States)
Schmidt, Johan A.
(Harvard Univ. Cambridge, MA, United States)
Baidar, Sunil
(Colorado Univ. Boulder, CO, United States)
Coburn, Sean
(Colorado Univ. Boulder, CO, United States)
Dix, Barbara
(Colorado Univ. Boulder, CO, United States)
Koenig, Theodore K.
(Colorado Univ. Boulder, CO, United States)
Apel, Eric
(National Center for Atmospheric Research Boulder, CO, United States)
Bowdalo, Dene
(York Univ. United Kingdom)
Campos, Teresa
(National Center for Atmospheric Research Boulder, CO, United States)
Eloranta, Ed
(Wisconsin Univ. Madison, WI, United States)
Evans, Mathew J.
(York Univ. United Kingdom)
Digangi, Joshua P.
(Princeton Univ. Princeton, NJ, United States)
Zondlo, Mark A.
(Princeton Univ. Princeton, NJ, United States)
Gao, Ru-shan
(National Oceanic and Atmospheric Administration Boulder, CO, United States)
Haggerty, Julie A.
(National Center for Atmospheric Research Boulder, CO, United States)
Hall, Samuel R.
(National Center for Atmospheric Research Boulder, CO, United States)
Hornbrook, Rebecca S.
(National Center for Atmospheric Research Boulder, CO, United States)
Jacob, Daniel
(Harvard Univ. Cambridge, MA, United States)
Morley, Bruce
(National Center for Atmospheric Research Boulder, CO, United States)
Pierce, Bradley
(National Oceanic and Atmospheric Administration Madison, WI, United States)
Reeves, Mike
(National Center for Atmospheric Research Boulder, CO, United States)
Romashkin, Pavel
(National Center for Atmospheric Research Boulder, CO, United States)
Ter Schure, Arnout
(Electric Power Research Inst. Palo Alto, CA, United States)
Volkamer, Rainer
(Colorado Univ. Boulder, CO, United States)
Date Acquired
September 1, 2016
Publication Date
July 1, 2015
Publication Information
Publication: Proceedings of the National Academy of Sciences
Volume: 112
Issue: 30
e-ISSN: 1091-6490
Subject Category
Meteorology And Climatology
Report/Patent Number
NF1676L-20964
Funding Number(s)
WBS: WBS 153351.05.04.01.05.02
Distribution Limits
Public
Copyright
Other

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