The Central Pollution Control Board said on Thursday that the countrywide “janata curfew” on March 22 and the 21-day lockdown imposed since March 24 to combat the coronavirus outbreak have resulted in a significant improvement in air quality in the country, PTI reported. The pollution has been reduced by travel restrictions and closure of industries.

“The major sectors contributing to air pollution are transport, industries, power plants, construction activities, biomass burning, road dust resuspension and residential activities,” the pollution watchdog said. “In addition, certain activities such as operation of DG sets, restaurant, landfill fires, etc. also contribute to air pollution.”

The Air Quality Index in Delhi at 4 pm was 69, in the “satisfactory” category, according to the board’s website. In normal times, the index often hovers in the “very poor” to “severe” category.

An index reading between 0 and 50 puts the air quality in “good” category. A reading between 51 and 100 puts it in the “satisfactory” category, between 101 and 200 in the “moderate” category, and between 201 and 300 in the “poor category”. The air quality is said to be “very poor” when the index value falls between 300 and 400. An index value between 400 and 500 puts the quality in the “severe” category.

According to the government-run System of Air Quality Weather Forecasting and Research, the Air Quality Index in Delhi at 5.06 pm was 62, in the “satisfactory” category. The organisation said that in Mumbai overall, the index stood at 76, in Pune at 52 and in Ahmedabad at 94.

India has so far registered 50 deaths from 1,965 confirmed coronavirus infections, according to the Union Ministry of Health and Family Welfare.