Halogen chemistry reduces tropospheric O<sub>3</sub> radiative forcing
Tropospheric ozone (O<sub>3</sub>) is a global warming gas, but the lack of a firm observational record since the preindustrial period means that estimates of its radiative forcing (RF<sub>TO<sub>3</sub></sub>) rely on model calculations. Recent observational evid...
Main Authors: | , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-01-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | http://www.atmos-chem-phys.net/17/1557/2017/acp-17-1557-2017.pdf |
Summary: | Tropospheric ozone (O<sub>3</sub>) is a global warming gas, but the lack of a
firm observational record since the preindustrial period means that estimates
of its radiative forcing (RF<sub>TO<sub>3</sub></sub>) rely on model calculations.
Recent observational evidence shows that halogens are pervasive in the
troposphere and need to be represented in chemistry-transport models for an
accurate simulation of present-day O<sub>3</sub>. Using the GEOS-Chem model we show
that tropospheric halogen chemistry is likely more active in the present day
than in the preindustrial. This is due to increased oceanic iodine emissions
driven by increased surface O<sub>3</sub>, higher anthropogenic emissions of
bromo-carbons, and an increased flux of bromine from the stratosphere. We
calculate preindustrial to present-day increases in the tropospheric O<sub>3</sub>
burden of 113 Tg without halogens but only 90 Tg with, leading to a
reduction in RF<sub>TO<sub>3</sub></sub> from 0.43 to 0.35 Wm<sup>−2</sup>. We attribute
∼ 50 % of this reduction to increased bromine flux from the stratosphere, ∼ 35 % to the ocean–atmosphere iodine feedback, and ∼ 15 % to increased tropospheric sources of anthropogenic halogens. This reduction of tropospheric O<sub>3</sub> radiative forcing due to halogens
(0.087 Wm<sup>−2</sup>) is greater than that from the radiative forcing of
stratospheric O<sub>3</sub> (∼ 0.05 Wm<sup>−2</sup>). Estimates of RF<sub>TO<sub>3</sub></sub>
that fail to consider halogen chemistry are likely overestimates
(∼ 25 %). |
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ISSN: | 1680-7316 1680-7324 |