Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 110, Issue 6, Pages 2035-2040Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1212386110
Keywords
atmospheric chemistry; oxidative capacity; halogens; heterogeneous chemistry; air-sea exchange
Categories
Funding
- National Center for Atmospheric Research/Earth Observing Laboratory
- ESRL/CIRES
- Fulbright fellowship
- National Science Foundation Faculty Early Career Development (CAREER) [ATM-0847793]
- National Science Foundation [NSF-AGS-1104104]
- California Air Resources Board [09-317]
- Department of Energy [DE-SC0006080]
- Electric Power Research Institute (EPRI) [EP-P27450/C13049, EP-P32238/C14974]
- Div Atmospheric & Geospace Sciences
- Directorate For Geosciences [1104179, 1104104] Funding Source: National Science Foundation
- Div Atmospheric & Geospace Sciences
- Directorate For Geosciences [0847793] Funding Source: National Science Foundation
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Atmospheric iodine monoxide (IO) is a radical that catalytically destroys heat trapping ozone and reacts further to form aerosols. Here, we report the detection of IO in the tropical free troposphere (FT). We present vertical profiles from airborne measurements over the Pacific Ocean that show significant IO up to 9.5 km altitude and locate, on average, two-thirds of the total column above the marine boundary layer. IO was observed in both recent deep convective outflow and aged free tropospheric air, suggesting a widespread abundance in the FT over tropical oceans. Our vertical profile measurements imply that most of the IO signal detected by satellites over tropical oceans could originate in the FT, which has implications for our understanding of iodine sources. Surprisingly, the IO concentration remains elevated in a transition layer that is decoupled from the ocean surface. This elevated concentration aloft is difficult to reconcile with our current understanding of iodine life-times and may indicate heterogeneous recycling of iodine from aerosols back to the gas phase. Chemical model simulations reveal that the iodine-induced ozone loss occurs mostly above the marine boundary layer (34%), in the transition layer (40%) and FT (26%) and accounts for up to 20% of the overall tropospheric ozone loss rate in the upper FT. Our results suggest that the halogen-driven ozone loss in the FT is currently underestimated. More research is needed to quantify the widespread impact that iodine species of marine origin have on free tropospheric composition, chemistry, and climate.
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