Evidence for strong, widespread chlorine radical chemistry associated with pollution outflow from continental Asia

The chlorine radical is a potent atmospheric oxidant, capable of perturbing tropospheric oxidative
cycles normally controlled by the hydroxyl radical. Significantly faster reaction rates allow chlorine
radicals to expedite oxidation of hydrocarbons, including methane, and in polluted environments, to
enhance ozone production. Here we present evidence, from the CARIBIC airborne dataset, for extensive
chlorine radical chemistry associated with Asian pollution outflow, from airborne observations made
over the Malaysian Peninsula in winter. This region is known for persistent convection that regularly
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delivers surface air to higher altitudes and serves as a major transport pathway into the stratosphere.
Oxidant ratios inferred from hydrocarbon relationships show that chlorine radicals were regionally more
important than hydroxyl radicals for alkane oxidation and were also important for methane and alkene
oxidation (>10%). Our observations reveal pollution-related chlorine chemistry that is both widespread
and recurrent, and has implications for tropospheric oxidizing capacity, stratospheric composition and
ozone chemistry.

The chlorine radical is a potent atmospheric oxidant, capable of perturbing tropospheric oxidative cycles normally controlled by the hydroxyl radical. Significantly faster reaction rates allow chlorine radicals to expedite oxidation of hydrocarbons, including methane, and in polluted environments, to enhance ozone production. Here we present evidence, from the CARIBIC airborne dataset, for extensive chlorine radical chemistry associated with Asian pollution outflow, from airborne observations made over the Malaysian Peninsula in winter. This region is known for persistent convection that regularly delivers surface air to higher altitudes and serves as a major transport pathway into the stratosphere. ... mehrOxidant ratios inferred from hydrocarbon relationships show that chlorine radicals were regionally more important than hydroxyl radicals for alkane oxidation and were also important for methane and alkene oxidation (>10%). Our observations reveal pollution-related chlorine chemistry that is both widespread and recurrent, and has implications for tropospheric oxidizing capacity, stratospheric composition and ozone chemistry.