Why a late Diwali coinciding with peak stubble burning may spell bad news

“Yes, it is a cause for concern. The past year was an unusual year when meteorology played a pivotal role in keeping the air quality in check. Additionally, there were a few more reasons such as a reduction in the number of fire counts in 2022 compared to the previous two-three years,” says Gufran Beig, chair professor, National Institute of Advanced Studies Bangalore, and founder project director, SAFAR – a national air quality initiative of the ministry of earth sciences.

Beig explains that La Nina and climate change induced relatively faster wind conditions and bursting firecrackers in the relatively warmer weather of October last year are unlikely to repeat this year - especially the La Nina effect, as we are in an El Nino phase and may not have the same advantage and a Diwali in warmer times. The first and second weeks of November are the peak period for stubble fires.

“In the past five years, pollution has peaked mostly in the November 6-7 period. If target-oriented, science-backed preemptive measures are in place, we may overcome this period,” Beig said.

When Diwali and stubble burning coincide

Environmental expert Chandra Bhushan agrees that there is a strong correlation between high pollution levels and Diwali coinciding with peak stubble burning. The AQI, he says, rises sharply when Diwali falls between October-end and November-end.

Citing data, Bhushan – founder-CEO of the International Forum for Environment, Sustainability & Technology – says the AQI was 337 in 2019 when Diwali was celebrated on October 27. Just from Punjab and Haryana, 16,336 stubble fires were reported on that day.

In 2020, Diwali was celebrated on November 14, when 80,660 stubble fires were recorded in the two states alone. The AQI on that day shot up to 414. In 2021, the AQI was 382 on November 4, Diwali day, when 27,276 stubble fires were recorded.

The year 2022 fared much better when an early Diwali on October 24 ensured better air in comparison; 6,977 stubble fires were recorded on a day when the AQI was 312. This year, Diwali is on November 12.

An AQI between zero and 50 is 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'.

A third expert said it is still quite uncertain how the weather will play out and if we could see untimely rain in the early parts of winter due to climate change. “Usually a late Diwali, concentrated crop residue burning during a dry spell, and calm and cool weather conditions spike pollution levels,” says Anumita Roychowdhury, executive director, research and advocacy, Centre for Science and Environment.

The level of the spike, however, will depend on the overall efforts to control pollution from all sources over time and the effectiveness of the emergency action, she says.

According to Beig, sustainable solutions are needed to avoid extreme events during winter when stubble burning is at its peak – keeping in mind the economy, farmers and health concerns.

Solutions to stop crop burning, Roychowdhury says, are known and supported but need to be made affordable and accessible. The money would need to be spent better to eliminate pollution from the source rather than diverting it towards expensive, temporary, and cosmetic action, she said.

Steps taken to address crop burning, including subsidy for farm equipment to manage paddy stubble or bio-remedial measures to turn crop residue into manure, have been only marginally successful.

Apart from stubble burning, burning of biomass for warmth is also a source of pollution in north Indian winters.

Biomass burning a major problem

Apart from stubble burning – which lasts for about two months – bio-mass burning for fuel, and heating, also causes a spike in pollution in winter when the wind is calmer, making it harder for pollutants to disperse.

Biofuel and biomass burning in rural areas is one of the topmost concerns around the year, Beig says. “Here, I am not talking about stubble burning during the kharif crop as it lasts just short of two months. Of course, it adds to the fury and is responsible for extreme episodes triggered by calm wind conditions and lower temperatures.”

The monsoon's withdrawal time always plays a critical role in air quality science. If the monsoon withdraws late when we have already entered the early phases of winter, it is not good news, Beig said. Monsoon withdrawal is accompanied by anticyclonic circulation, which tends to slow down the winds, trapping pollutants. If this happens when the temperatures are lower, then the winds become more stagnant or slow, he says.

Bio-mass burning, mostly for heating purposes is one of the key culprits in winter, agrees Bhushan. “Cooking fuel is getting cleaner as more people now have access to cooking gas, PNG, biogas, etc. But biomass for heating is a major issue in the Indo-Gangetic plans when it gets colder and needs to be tackled in right earnest.”

Action beyond Delhi-NCR

The Delhi government recently introduced a slew of measures such as teams to tackle dust pollution, a war room to monitor pollution, a ban on firecrackers, etc. Chief minister Arvind Kejriwal had also floated the idea of cloud seeding to induce artificial rain.

The Supreme Court has asked the Commission for Air Quality Management (CAQM) to submit a report on the measures being implemented to combat air pollution in Delhi and nearby areas.

The Graded Response Action Plan (GRAP), which comprises four categories of anti-air-pollution measures, is now forecast-based unlike earlier when norms were enforced when the AQI worsened.

But most of these actions are limited to Delhi or its surroundings and all norms go for a toss in other parts of the northern plains, where air pollution is a major issue.

According to Roychowdhury, tackling pollution requires equally stringent efforts across Delhi-NCR and beyond. Winter action is usually about immediate emergency response and enforcement measures such as controlling dust and stopping waste burning and diesel gensets to ensure the problem does not aggravate.

The real solution, Roychowdhury says, will emerge from 100 percent segregation and treatment of all waste streams, massive transition to clean fuels in all industrial areas and all households, upscaling of integrated public transport infrastructure to reduce traffic on road, and fleet electrification among the priority measures.

Beig says the state authorities or CAQM's efforts are praiseworthy. However, the steps and actions should be target-oriented and science-based. For example, Delhi faces a more acute problem of tiny PM2.5 particles that can penetrate deep inside our bodies. So the first priority should be to check that. Dust has some amount of PM2.5 but mostly contains the coarser PM10 particles.

“If we are prioritizing dust control, are we addressing the coarser particles or the dangerous tiny particles?” So the goal and priority should be long-term sustainable solutions rather than short-term piecemeal steps, Beig says.

Due to its typical climatology and geographical location, Delhi gets a significant share of external pollution, which varies from season to season, Beig explains.

According to results published using India’s first indigenously developed air quality forecasting model framework, SAFAR, the external share in Delhi’s PM2.5 pollution during the peak winter season of November-December may vary between 30-40 percent on an average or even more on some typical episodes.

This not only includes stubble burning but a lot more other sources outside Delhi's limits such as biofuel, wood, charcoal, dung, brick kilns, etc. “So addressing emission in the surrounding region is one of the keys to controlling Delhi’s air pollution,” Beig says.

What about cloud seeding to induce artificial rain when pollution spikes? Both Bhushan and Beig feel cloud seeding may not be a good idea as it is a stop-gap measure.

Artificial rain induced by cloud seeding, according to Beig, has been used and found to be partially successful in curtailing high pollution events. But there is a rider – naturally produced seeding clouds have to be present.

“If clouds are not there, what will you seed? You cannot take millions of gallons of water in aircraft to produce rain. Besides, we usually do not see seeding clouds in November or during winter in Delhi.”

In 2020, Diwali was celebrated on November 14, when 80,660 stubble fires were recorded in Punjab and Haryana alone. The AQI on that day shot up to 414. In 2021, the AQI was 382 on November 4, Diwali day, when 27,276 stubble fires were recorded. This year, Diwali is on November 12. (Photo by Suvan Chowdhury via Pexels)

Wind to the rescue

So are the measures introduced by CAQM over time responsible for the better air quality in the past year or is it the weather god again? Or a combination?

It's a combination, says Beig. “Yearly gross emissions have increased since 2011 but we have seen a marginal improvement in air quality of Delhi in recent times.” This, he says, can be attributed to timely temporary interventions to curtail emissions at source and reduce the magnitude of particulate matter concentration, whether it is PM2.5 or PM10. Such action reduces the annual or monthly averages during the peak seasons.

In recent times, however, climatology has often been unusual and abrupt. “Such uncertain abrupt conditions can go either way in terms of changes in air quality,” Beig says.

For example, the 2022-23 winter saw predominantly moderate wind speed conditions, particularly at night, which dispersed pollutants. This reversal towards relatively faster winds in north India is understood to be an indirect impact of the century’s first triple-dip La Nina, an artifact of the changing climate, Beig says.

Till the first week of October this year, Delhi recorded 200 days of 'good to moderate' air quality. In comparison, the number during the corresponding period in 2022, 2021 and 2019 stood at 154, 183 and 174, respectively.

Bhushan too says Delhi has been experiencing good air days in the past year more because of favourable meteorological conditions. He, however, feels the government seems to be serious as we are now talking about air pollution all around the year and not just in winter. “Though we are moving in the right direction, speed is required as there is a gap between what should be done and what is being done.”

Sunil Dahiya, analyst, Centre for Research on Energy and Clean Air, says the need of the hour is strict action that goes past the policy stage and is implemented on the ground. "Air pollution will start rising due to episodic biomass burning, building on top of existing sources such as transportation, thermal power plants, industries, etc. With increasing awareness, however, the levels might not touch the previous highs.”