While the affidavit (which FactChecker has access to) said the contribution was 4% in winters and 7% in summers, another section in the same affidavit said that paddy stubble burning contributed 35-40% to the capital's particulate matter (PM) 2.5 and PM 10 concentrations. This caused an outcry among sections of the media and experts in the air pollution domain on the actual contribution of stubble burning to Delhi's severely deteriorating air quality.

Adding to the confusion in the variation of figures, solicitor general of India, Tushar Mehta, in his oral submission of the affidavit, said that the stubble burning figure was less than 10%, Bar and Bench reported. There hasn't been, thus far, a definite answer regarding the contribution of stubble burning to Delhi's air pollution.

Environment policy experts FactChecker spoke to said that it all boils down to the interpretation of data. They emphasized that although stubble burning is not the main cause of pollution during all of winter, it is definitely an episodic problem. This means that it significantly adds to air pollution during the crop-burning season which happens between the start of October and mid-November each year.

Stubble burning is the large-scale burning of crop residues from the rice–wheat systems of Punjab, Haryana and western Uttar Pradesh, according to the Centre for Science and Environment (CSE).

But before we delve into the contribution of stubble burning to Delhi's pollution, it's worth noting what data the central government excluded while submitting their affidavit to the SC.

Data on Agricultural Burning for October Not Included

The centre said that the data was sourced from a scientific study but did not disclose the name, organisation or time period of the study. However, the government cited an August 2018 study conducted by The Automotive Research Association of India (ARAI) and The Energy and Resources Institute (TERI) which was prepared for the Department of Heavy Industry Ministry under the Ministry of Heavy Industries and Public Enterprises of the government of India, Bhargav Krishna, fellow at Delhi-based Centre for Policy Research (CPR), told FactChecker via email.

The study, titled "Source Apportionment of PM2.5 & PM10 of Delhi NCR for Identification of Major Sources" collected data between April and June 2016 (summer period) and November 2016 and February 2017 (winter period) at 20 locations in Delhi but left out the month of October. The study specifically mentions, "It is to be noted that the contribution of agricultural burning is not fully accounted for in this study as the monitoring and modelling periods did not include the month of October, when the burning activities are generally at their maximum." Moreover, the study says that the figures were averaged for the entire period (including summers) and hence, "do not highlight the contribution of agricultural burning, which happens during a certain number of days and cause episodically high pollutant concentrations".

"Stubble burning is a seasonal problem, and in the period that it is prevalent, can cause anywhere between 20-50% the overall air pollution loading," said Krishna. "If you average out all the sources over the period of a year, the contribution of stubble burning and other biomass burning would come down further."

Besides, the government's own real-time data published by System of Air Quality and Weather Forecasting And Research (SAFAR) and The Central Pollution Control Board (CPCB) show a much higher figure. SAFAR's data show that the daily contribution varied between 7% on November 1 to 48% on November 7, 2021 with the latter figure being the highest till date this year. These dates coincide with this year's Diwali celebrations which clearly add to the pollution but there is also another reason for the rise in pollution. "After Diwali, there was a sudden spike in pollution levels but we expected this for the simple reason that during October we had a lot of rains which in turn deferred the burning of crops," Anumita Roy Chowdhury, executive director, research and advocacy at CSE, told FactChecker.

Stubble Burning Only an Episodic Contribution to Pollution

The data by SAFAR is highly variable on a daily basis, according to Chowdhury. "It can range from 1%-4% on some days, going upto 20%, and on some days hitting 30-40%. But it's not consistently high at all," she said. This is true because there were 1,797 fire counts on November 2 while the share of stubble fires to Delhi's air pollution was around 7%; whereas on November 8, 5,450 fire counts were reported, sharply increasing the share of stubble fires to 48% around that period. The overall air quality during this peak period also fluctuated from 300 PM10 in the 'poor' category to 551 PM10 in the 'severe' category. Experts also said that the speed and direction of the wind and the intensity of the burning played a major role in pollution levels in Delhi.

Further, Chowdhury said that this is only one phase of the season. If you take the entire winter into consideration, the proportion comes down even further. Because crop burning does not happen everyday, she said. "Also, it's not a round-the-year problem. And if we check figures for the whole year, the proportion is going to be really small. Hence crop burning is only an episodic problem in Delhi," she explained.

Experts also focussed on major sources other than agricultural fires that contributed significantly to air quality deterioration in Delhi and National Capital Region (NCR). As per CSE's analysis of total pollution sources to PM2.5 in Delhi between October 24 and November 8, 2021, the capital's local sources reported 31%, of which Delhi's transport sector accounted for more than half (51%) of its local pollution sources. This is followed by household pollution (13%), industries (12%) and construction (7%).

Experts said that even if we stop stubble burning completely, considering the crop burning season's average contribution of 30%, Delhi's AQI [Air Quality Index] would come down from 450 plus to 300, which would still fall under the 'poor' category. "The situation today is that if AQI is around 200-250, we feel happy, while we should worry that it's manifold higher than the air quality guidelines," Sagnik Dey, associate professor at the Centre for Atmospheric Sciences, Indian Institute of Technology (IIT), Delhi, told FactChecker.

"We all were happy when the lockdown improved the air quality, but we did not fully understand the implications of the air quality level not remaining below our NAAQS (National Ambient Air Quality Standards) throughout the lockdown," said Dey, adding, "That itself indicated that the background level pollution is very high and unless year round efforts are made, we would not be able to improve the situation."

Workable Alternatives to Stubble Burning

Experts said that the stubble burning issue is a byproduct of decades of poor policy-making. Current air pollution policies are largely aimed at tackling episodic high-exposure events, said Krishna of CPR. "Whether it be the retroactive application of GRAP [Graded Response Action Plan- emergency measures to be taken to reduce pollution], ineffectual smog towers or ad-hoc measures like diverting truck traffic around the capital; these are all sticking plasters on a gaping wound that needs long-term care and attention," he said. Although GRAP was mentioned in emergency measures, the centre also listed long-term measures taken by them to the SC. These include Ambient Air Quality Monitoring Network, air quality forecast and measures for control of vehicular, industrial and waste emissions

Further, Chowdhury and Dey said that in-situ and ex-situ management practices should be implemented fully and equipment such as happy seeders, hay rakes, and straw choppers be made available to all farmers. For in-situ management, farmers mix the stubble back into the soil so that they do not have to burn it. While in ex-situ one can collect the straw and use it for something else such as generating power, etc., said Chowdhury. "But all this is very infrastructure centric. The government has to build the infrastructure and access points so that it is scalable across regions. At the same time, when we specifically look at Delhi and NCR we have to focus on local sources of pollution. Although it's important to zero down on Delhi-NCR, we need a regional, integrated and scaled-up source-wise approach," she concluded.

To avoid reaching episodic peaks, Krishna suggested that actions planned under mechanisms such as GRAP be engaged proactively. "We already have AQ forecasts from IITM-SAFAR and Urban Emissions among others, surely we can use them to apply measures such as power plant closures, construction bans, etc.," he said.

Alternatives, again in this case, must be well thought through, and cannot simply be techno-fixes that address the "here and now" but focus on long-term transitions in cropping patterns that align with the economic needs of farmers in these regions, Krishna suggested