Satellite data published by National Aeronautics and Space Administration (NASA) has revealed that air pollution over northern India has plummeted to a 20-year-low for this time of the year.

NASA’s satellite sensors have found that aerosol levels are at a 20-year low post the nationwide lockdown.

‘We knew we would see changes in atmospheric composition in many places during the lockdown. But I have never seen aerosol values so low in the Indo-Gangetic Plain at this time of year,’ NDTV quoted Pawan Gupta, a Universities Space Research Association (USRA) scientist at NASA’s Marshall Space Flight Center, as saying.

Satellite data show that levels of airborne particles over northern #India have dropped significantly since the #COVIDー19 lockdown began. https://t.co/xz6NgbQLOW pic.twitter.com/aP0fi5vL64

— NASA Earth (@NASAEarth) April 21, 2020

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite retrieved the data.

The published data shows aerosol optical depth (AOD) in 2020 compared to the average for 2016-2019. AOD is basically a measure of how light, while traveling through the atmosphere, is absorbed or reflected by airborne particles.

It was difficult to observe a change in the pollution signature in the first few days of the lockdown.

‘We saw an aerosol decrease in the first week of the shutdown, but that was due to a combination of rain and the lockdown,’ Gupta said.

Aerosol concentrations usually increase after heavy precipitation, and it rained heavily over vast areas of northern India around March 27, helping in clearing the air of aerosols.

‘After the rainfall, I was really impressed that aerosol levels did not go up and return to normal. We saw a gradual decrease and things have been staying at the level we might expect without anthropogenic emissions,’ Gupta said.

In southern India, however, aerosol levels have not yet decreased to the same extent.

‘This is a model scientific experiment,’ Robert Levy, program leader for NASA’s MODIS aerosol products, said about the lockdown and how it has affected pollution.

‘We have a unique opportunity to learn how the atmosphere reacts to sharp and sudden reductions in emissions from certain sectors. This can help us separate how natural and human sources of aerosols affect the atmosphere,’ Mr Levy added.

Also Read: Coronavirus Lockdown: With Humans Indoors, Pollution Levels Drop, Ozone Layer Heals