There can be no arguing that stubble burning is a major contributor to the bad air in Delhi at this time of the year, just as there can be no arguing that Delhi’s average annual air quality index (AQI) is in the poor or the upper end of the moderate category.
This may seem to be at odds with the claims made in an affidavit submitted by the environment ministry in the Supreme Court that downplays the contribution of stubble burning to the Capital’s bad air. The affidavit is clearly an example of the damage averages can wreak on policy making when used without context.
The facts are thus.
One, Delhi always has bad air.
In 2018, the average AQI was 225.4; in 2019, it was 214; in 2020, it was 185.2; and in 2021, till November 14, it was 188.2. The number of stations measuring AQI across these years is not the same, but the metric is still a good indicator of how good (or bad, in this case) Delhi’s air was.
Two, stubble burning just serves to push the AQI into the very poor (300-400) or severe (400-500 ) category.
For instance, between October 20 and November 14 this year, Delhi’s AQI has been in the severe zone on seven days. On each of these days, the contribution of farm fires to Delhi’s PM2.5 contribution was between 26%-48%.
This isn’t an aberration.
For instance, according to a paper, “Objective evaluation of stubble emission of North India and quantifying its impact on air quality of Delhi”, in the first fortnight of November 2018, the contribution of stubble burning (biomass) to AQI was 9, 10, 30, 58, 29, 9, 10, 8, 7, 13, 22, 24, 5, 9, and 29%. That’s an average of around 18%.
Three, Delhi doesn’t see that many days when the AQI is severe.
Given that Delhi’s AQI has been in the severe category on a maximum of 25 days (in one year) in the period between 2016 and 2020 according to an affidavit filed by the environment ministry in the Supreme Court – including days when AQI was very poor, the number was 64 in 2020 and 80 in 2019 – it is clear that stubble burning has a clear impact on the Capital’s air. Long-term interventions – more public transport, better garbage disposal, moves to combat desertification, electric vehicles – will be needed to get Delhi’s average AQI down, but it is clear that short-term interventions (combating stubble burning, for one) will be needed to keep it from slipping into the very poor and severe categories.