What can solve Delhi’s air pollution problem?


Not everything is judicially manageable, the Supreme Court said on Thursday as it declined to grant an urgent hearing to a petition demanding fresh guidelines on stubble burning and other crucial steps to curb the rising pollution in Delhi and surrounding areas. The petition was asking for multiple directions from the court, but its focus is on fixing stubble burning. An HT analysis of various statistics related to Delhi’s pollution shows that while banning stubble burning will clearly help, it cannot offer a complete fix to the problem. Here are three charts that explain this in detail.

Anybody who argues stubble burning is not a major pollutant is lying

Because there are multiple source-apportionment studies – they estimate contribution of various pollutants – some sections cite numbers to argue that stubble burning is not a major pollutant as far as Delhi’s air pollution problem is concerned. This is a disingenuous argument. The real impact of stubble burning on Delhi’s air matters not just on the intensity of the activity (satellite data gives us number of farm fires) but also metrological conditions, especially wind direction and speed. To put things simply, if the wind is blowing from east to west rather than west to east, stubble burning in Punjab will increase pollution in Pakistan rather than Delhi. Similarly, a high wind speed leads to faster dispersal of pollutants from farm fires. When these metrological factors turn adverse from Delhi’s perspective, the pollution problem becomes worse even for a lower intensity of stubble burning.

For example, they were responsible for half (48%) of Delhi’s PM2.5 on November 7 last year, although the number of fires that day (4,997) was lesser than two days earlier (6,531), when they contributed 36% to Delhi’s PM2.5. In the peak stubble-burning season, farm fires have a significant contribution to Delhi’s air pollution.

See Chart 1: contribution of stubble burning to Delhi’s pollution

However, Delhi sees very bad air pollution days even without stubble burning

This becomes clear if one reads the number of active fires in Punjab and Haryana with the AQI in Delhi in November 2021. From November 5 to 13, there were more than 4,000 fires on all days but one. Expectedly, the AQI in Delhi was in the “severe” range (above 400) on seven of those nine days. On the other hand, the AQI was severe even in the November 26 to November 28 period, even though only 120, 75, and 20 farm fires were recorded on these days respectively. This shows that while a ban on stubble burning will certainly help, it is no guarantee of no “severe” days.

See Chart 2: Delhi AQI and number of farm fires

An effective anti-pollution policy should set the bar higher

According to the daily AQI bulletin of the Central Pollution Control Board (CPCB), Delhi’s air has been in the “poor” category or worse on 52% of the days from 2016 to November 8 this year. To be sure, winter is not the only period when Delhi has an air pollution problem. In fact, even in summer months (April to June), the air has been in the “poor” category or worse on 48% of days since 2016. The ratio increases to 55% if one excludes 2020, when air quality improved drastically because of the 68-day nationwide lockdown. This “poor” threshold is important because this is when the air start affecting almost everyone exposed to it for long, and not just the people with lung or heart diseases.

See Chart 3: distribution of days by AQI category in Delhi since 2016

And that requires a pro-active rather than reactive policy

To be sure, there seems to be some agreement between different governments and authorities that stubble burning is not the only cause of the winter pollution. This can at least be seen from the Graded Response Action Plan (GRAP), which also restricts industrial activity, construction, and sprinkles water on road to reduce dust among other things in anticipation of a deterioration in air quality. However, as its name suggests, the restrictions on this plan kick in response to emergency-like situations, and there is little attention given to fixing those problems long-term. Delhi’s year-round air pollution data shown above illustrates why that is harmful.