Every year it’s a common phenomenon that a dirty haze appears over South Asia and China, including North India, between December and March. The haze is a mixture of pollutants which are borne out of residual crop burning, emissions of vehicles, industrial pollution, and biomass fuel burning, known as Asian Brown Cloud. However, as monsoon approaches, the brown cloud vanishes.

But what happens to the pollutants present in the air? A team of scientists from Cyprus and Germany, after their 2 decades of research, have discovered that the Indian monsoon cleans the large lumps of pollutants gathered from the atmosphere.

The lead researcher, Jos Lelieveld who is the head of the Max Planck Institute for Chemistry in Germany reckoned the Indian monsoon as two-faced. As the summer ends, dark clouds collect moisture from the Arabian Sea and Bay of Bengal every year and proceed towards land, which indicates the arrival of monsoon. Although above this stormy layer is a layer with a clear atmosphere and devoid of clouds. This is known as the anti-cyclone. With every monsoon, a larger layer of anti-cyclone is accompanied.

While the monsoon envelops sub-continent, building a dense layer of clouds, the anti-cyclone accompanying the monsoon covers a much larger area, stretching from the Mediterranean Sea to the Pacific Ocean. In addition to moisture, Indian monsoon accumulates pollutants hovering in the atmosphere throughout the dry season and thrusts it higher into the anti-cyclone.

As found by Lelieveld and his team, Indian monsoon pushes most of the pollutants away from the immediate atmosphere into the anti-cyclone. The toxic parts of nitrogen, hydrogen oxides, sulfur and a lot of other pollutants are removed naturally by the chemicals present in the anti-cyclone. Remains are then pushed down to the monsoon and washed clean by rains.

Thus, it can be concluded that monsoon plays a significant role in chemically processing and removing pollutants from the atmosphere.

Picture Credits: Rajarshi Mitra

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