According to the satellite data published by which agency stated that the air pollution over northern India has dropped to a 20-year-low for this time of the year?

According to the satellite data published by which agency stated that

1.	According to the satellite data published by which agency stated that the air pollution over northern India has dropped to a 20-year-low for this time of the year?
Answer» According to the satellite data published by US space agency National Aeronautics and Space Administration (NASA) stated that the air pollution over northern India has dropped to a 20-year-low for this time of the year. The data were retrieved by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite.As per the analysis, an optical depth or thickness of less than 0.1 over the entire atmospheric vertical column shows a "clean" condition. If aerosols are concentrated near the surface, an optical depth of 1 or above indicates very "hazy" conditions.