Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 112, Issue 30, Pages 9281-9286Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1505142112
Keywords
atmospheric chemistry; oxidative capacity; halogens; heterogeneous chemistry; UTLS
Categories
Funding
- National Science Foundation (NSF) [AGS-1104104]
- NSF
- Fulbright Junior Research Award
- Earth System Research Laboratory/Cooperative Institute for Research in Environmental Sciences graduate fellowship
- National Science Foundation Faculty Early Career Development Award [ATM-0847793]
- Department of Energy [DE-SC0006080]
- Electric Power Research Institute [EP-P27450/C13049, EP-P32238/C14974]
- NASA
- Danish Council for Independent Research \ Natural Sciences
- Natural Environment Research Council [ncas10006, 1232509, NE/K004603/1] Funding Source: researchfish
- NERC [NE/J00619X/1, NE/K004603/1, ncas10006] Funding Source: UKRI
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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 (O-3), oxidize mercury, and modify oxidative capacity that is relevant for the lifetime of greenhouse gases. Most of the tropospheric O-3 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 degrees N to 40 degrees S), and show that these halogens are responsible for 34% of the column-integrated loss of tropospheric O-3. The observed BrO concentrations increase strongly with altitude (similar to 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 (Br-y), 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 O-3 needs to be considered when estimating past and future ozone radiative effects.
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