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The South Asian monsoon—Pollution pump and purifier

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Science  14 Jun 2018:
eaar2501
DOI: 10.1126/science.aar2501

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Abstract

Air pollution is growing fastest in monsoon-impacted South Asia. During the dry, winter monsoon the fumes disperse toward the Indian Ocean, creating a vast pollution haze, but their fate during the wet, summer monsoon has been unclear. We performed atmospheric chemistry measurements by aircraft in the “Oxidation Mechanism Observations” campaign, sampling the summer monsoon outflow in the upper troposphere between the Mediterranean and the Indian Ocean. The measurements, supported by model calculations, show that the monsoon sustains a remarkably efficient cleansing mechanism in which contaminants are rapidly oxidized and deposited to Earth’s surface. However, some pollutants are lofted above the monsoon clouds, and chemically processed in a reactive reservoir before being redistributed globally, including to the stratosphere.

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