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Title: Active and widespread halogen chemistry in the tropical and subtropical free troposphere

Halogens 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 (10°N to 40°S), 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 (~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 themore » 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. Lastly, the halogen-catalyzed loss of tropospheric O3 needs to be considered when estimating past and future ozone radiative effects.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [3] ;  [3] ;  [4] ;  [5] ;  [4] ;  [6] ;  [5] ;  [7] ;  [8] ;  [9] ;  [4] ;  [4] ;  [4] ;  [10] ;  [4] ;  [11] more »;  [4] ;  [4] ;  [12] ;  [3] « less
  1. Univ. of Colorado, Boulder, CO (United States); The Hong Kong Univ. of Science and Technology, Hong Kong (China)
  2. Harvard Univ., Cambridge, MA (United States); Univ. of Copenhagen, Copenhagen (Denmark)
  3. Univ. of Colorado, Boulder, CO (United States)
  4. National Center for Atmospheric Research, Boulder, CO (United States)
  5. Univ. of York, York (United Kingdom)
  6. Univ. of Wisconsin, Madison, WI (United States)
  7. Princeton Univ., Princeton, NJ (United States); National Aeronautics and Space Administration, Hampton, VA (United States)
  8. Princeton Univ., Princeton, NJ (United States)
  9. National Oceanic and Atmospheric Administration, Boulder, CO (United States)
  10. Harvard Univ., Cambridge, MA (United States)
  11. National Oceanic and Atmospheric Administration, Madison, WI (United States)
  12. Electric Power Research Institute, Palo Alto, CA (United States)
Publication Date:
Grant/Contract Number:
SC0006080; EP-P27450/C13049; EP-P32238/C14974; 0602-02530B; 15121680
Type:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 112; Journal Issue: 30; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Research Org:
Univ. of Colorado, Boulder, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 54 ENVIRONMENTAL SCIENCES; atmospheric chemistry; oxidative capacity; halogens; heterogeneous chemistry; UTLS
OSTI Identifier:
1235122
Alternate Identifier(s):
OSTI ID: 1348399