NARL scientists solve mystery over unequal aerosol distribution

A study by the National Atmospheric Research Laboratory (NARL) in Gadanki in Chittoor district has solved the mystery over the unequal aerosol distribution in the atmosphere in India and China.

Published in the recent issue of the Nature magazine, a research paper brought out by a team led by Scientist-SF M. Venkat Ratnam is expected to change the narrative over the rainfall prediction pattern and the impact of aerosols on health. Aerosols are known to be caused by crop residue burning, forest fires, rapid urbanisation and industrialisation. Studieshave pointed to the effect of the enhanced man-made emissions on the Asian monsoon circulation and the resultant precipitation over East and South East Asia. A ‘Dipole pattern’ in Aerosol Optical Depth (AOD), based on long-term satellite measurements, indicated a concurrent increase over India and a marked reduction over China.

The study observed a rapid increase in aerosol loading over India and its adjoining seas, and in sharp contrast, reduction over China, which is credited to the country’s ‘clean air actions’.

Scientists at NARL, a unit of the Department of Space, have found decreasing trends in the surface (black carbon) aerosol concentration in the recent decade. “It appeared as a surprise in the first glance, but similar decreasing trends were noticed over several locations in India,” Dr. Venkat Ratnam told The Hindu over telephone.

The pollutants over the earth’s immediate surface are easily lifted to the free troposphere through convection and upward vertical velocities, leading to higher aerosol concentration farther from the earth, added the Shanti Swarup Bhatnagar awardee.

Global warming

The increased aerosol concentration over India is attributed to land aridity due to global warming, a 20% increase in fire activity and more than 50% rise in aerosol loading in the Thar Desert, southwestern Asia and northeastern Africa over the last decade.

Interestingly, decreasing trends in AOD were observed in northwestern India, which is credited to conversion of deserts into crop-land areas.

NARL Director A.K. Patra said the study would have significant consequences on the background meteorology.

“Depending on the aerosol type, they can modify the cloud condensation nuclei (CCN) activity, thus affecting convection and/or precipitation process,” Dr. Patra noted.

The NARL is currently obtaining chemical compositions at different altitudes to check for any change in the trends.

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