Enter the Smog: As smog descends on Indian cities, see what the data really says

Is Delhi truly the epicentre of India’s air quality crisis? Is the air in other cities in the central-north region just as bad? Are there southern cities with equally bad air quality? As smog descends on Indian cities, we try to see what the data really says.

Indian cities among most polluted
WHO found that 13 of the 20 cities with the worst air quality in 2018 were in India (after averaging annual PM 2.5 absolute concentration across cities)

Bad air report from Delhi stations
Between November 5, 2018, and November 5, 2019, 9 of 10 pollution watch stations that recorded the worst air quality were in Delhi. The first station outside the central-north belt to show up on the list was in Kolkata, at 48th spot, and the first southern station was in Chennai, at 73rd place.

It’s all seasonal in Delhi
The seasonality of Delhi’s bad air is significant. Wazirpur, which had the worst annualised air quality over November 2018-2019, had a clean air window from July to September.

South breathes easy
Does the air quality index in other cities ever reach Delhi-like levels? In winter, Kolkata comes close. Chennai, Mumbai and Hyderabad are largely in the safe zone throughout the year.

Most cities face bad air
Most cities score poorly on the air quality index (AQI). The only difference is that the number of hazardous days are lower when Wazirpur, Delhi compared with Delhi.

PM2.5 (monthly average) No. of days between November 2018 & 2019 with poor AQI (station reading)