Air pollution over North India has plummeted to a 20-year-low for this time of the year, according to satellite data published by US space agency National Aeronautics and Space Administration (NASA).
The US agency's satellite sensors observed aerosol levels at a 20-year low post the countrywide lockdown, implemented to slow the spread of the novel coronavirus.
'We knew we would see changes in atmospheric composition in many places during the lockdown,' said Mr. Pawan Gupta, a Universities Space Research Association (USRA) scientist at NASA's Marshall Space Flight Center. 'But I have never seen aerosol values so low in the Indo-Gangetic Plain at this time of year,' he added.
Acting US Assistant Secretary of State for South and Central Asia,Ms. Alice G Wells tweeted, 'These images from NASA were taken each spring starting in 2016 and show a 20-year low in airborne particle levels over India. When India and the world are ready to work and travel again, let's not forget that collaborative action can result in cleaner air.'
The data published with maps show aerosol optical depth (AOD) in 2020 compared to the average for 2016-2019. Aerosol optical depth is a measure of how light is absorbed or reflected by airborne particles as it travels through the atmosphere.
If aerosols are concentrated near the surface, an optical depth of 1 or above indicates very hazy conditions. An optical depth, or thickness, of less than 0.1 over the entire atmospheric vertical column is considered 'clean.' The data were retrieved by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite.
In the first few days of the lockdown, it was difficult to observe a change in the pollution signature. 'We saw an aerosol decrease in the first week of the shutdown, but that was due to a combination of rain and the lockdown,' said Mr Gupta.