New Delhi (CNN) For years, northern India -- especially the capital New Delhi -- has been battling air pollution with levels hitting the hazardous mark during the winter season.

In a series of maps, NASA plotted the aerosol levels in northern India during the same six-day period of March 31 to April 5 from 2016 to 2020.

"We knew we would see changes in atmospheric composition in many places during the lockdown," said Pawan Gupta, a Universities Space Research Association scientist at NASA's Marshall Space Flight Center in Huntsville, Alabama. "But I have never seen aerosol values so low in the Indo-Gangetic Plain at this time of year."

The Indo-Gangetic Plain stretches across the north of India.

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