Opinion Warmer weather, timely monsoon withdrawal meant slightly better air around Diwali. But worse is to come
Delhi’s air pollution crisis is complex and persistent. The only viable path is to tackle the root cause -- source emissions.
The cool November-December period is now likely to coincide with the delayed peak of
stubble burning. 
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Winter in Delhi is a season of contrasts: The glow of festivals, the chill of misty mornings, and the creeping dread of polluted skies. The past few months have offered a glimmer of hope with clear horizons, but an anxiety about what lies ahead lingers. Beneath that record clear horizon, I found no deeper meaning – it could be ascribed to record rainfall, and nothing more. Scientifically, there are multiple possibilities ahead. However, for once, the odds may tilt slightly in favour of relatively better air, thanks to ocean and large-scale circulation.
In recent years, delayed monsoon withdrawals have become a troubling new normal, widely linked to climate change by researchers. SAFAR’s earlier studies have shown that such delayed retreat, followed by the anti-cyclonic circulation that tends to slow down the winds beneath, gets further support under colder temperatures, leading to subsiding air and a compressed boundary layer. This dynamic acts like a lid over the city, allowing pollutants to accumulate ceaselessly. This year, however, was a welcome exception. The 2025 monsoon officially withdrew from Delhi at the beginning of the last week of September — the earliest retreat since 2002. The benefits were twofold. First, the early retreat under relatively warmer conditions kept the winds active, preventing the accumulation of pollutants near the surface. Second, post-withdrawal spells of western-disturbance-induced rainfall continued to wash the air, further curbing pollution build-up. In a region where late-monsoon retreat has become the new normal, 2025 stands out as a reminder of how seasonal timing and circulation dynamics can decisively alter the air quality trajectory.
India is presently under El Niño-Southern Oscillation (ENSO)-neutral conditions. However, the equatorial Pacific sea surface temperatures are trending below normal, signalling a likely transition towards a La Niña phase, with a 71 per cent probability by mid-October 2025. Forecasts suggest that the upcoming La Niña may initially remain weak, though a faster intensification later in the season could prove beneficial for North India’s air quality. Recent studies from the National Institute of Advanced Studies (NIAS) indicate that strong La Niña events enhance surface wind speeds over northern India, promoting greater dispersion, thereby reducing the build-up of fine particulates that typically lead to winter smog conditions. In essence, while the transition towards La Niña is still unfolding, its potential strengthening holds a silver lining for cleaner winter skies in Delhi.
Punjab and Haryana experienced some of the most severe floods in decades this September, likely delaying the harvest by one to two weeks. This shift postponed the peak of stubble burning, preventing it from coinciding with Diwali. Diwali fell earlier this year, when the temperature was relatively warm and the weather conditions were less hostile. This science led me to predict and provide an outlook that Delhi could avert the extreme smog events that have plagued it in past years, with a caveat that other ground realities remain the same.
A weak La Niña could also have counterproductive effects. If its link with climate change holds, the winter may be prolonged and severe, creating conditions that favour pollution accumulation and extreme smog events. Compounding this, heavy rains have already delayed the paddy harvest in Punjab and Haryana. The cool November-December period is now likely to coincide with the delayed peak of stubble burning.
The Rabi sowing pressure is a looming challenge. Farmers usually have around 45 days to clear fields — a tight window to begin with. In much of Punjab and Haryana, fields remain waterlogged or crops damp, delaying harvest by at least one to two weeks. This shortens the window for wheat sowing. Rice stubble adds to the challenge: Unlike wheat stubble, it cannot be fed to cattle due to high silica content and must be removed from the field. Without suitable alternatives, many farmers may resort to burning.
The judiciary, in a balanced move, relaxed the blanket ban and allowed the use of green firecrackers in the Delhi–NCR region — albeit under stringent conditions. While these so-called eco-friendly crackers marked some progress, they still emit 60-70 per cent of the pollutants that conventional fireworks do. So, with firework activity up by just 40 per cent, we have circled right back to where we started. The lesson is clear: Without diligent implementation, even the best-intentioned measures fizzle out. On the night of the celebration, pollution levels spiked sharply. Yet, by October 21, the overall AQI was “very poor”, not “severe”. That may sound like better news, but it was the weather, not anything else, doing the heavy lifting. Moderate winds and a warming morning sun aided dispersion, scrubbing the air faster than expected. Stations close to dense residential zones still recorded the worst numbers, a reminder that emissions are ultimately a neighbourhood story. But questions linger. What if the missing midnight-to-4 am data of many stations had been accounted for, the very window when pollution typically peaks under colder, calmer conditions? And what if the AQI algorithm could have capped 24-hour averaged concentrations to an equivalent AQI of 500, instead of capping at each hourly concentration at an AQI of 500, potentially masking the true extent of the night’s pollution? In some locations, hourly concentrations soared to an astonishing 1000-1800 µg/m³ after midnight. The numbers tell a story, but only if we’re willing to read between the lines of smoke.
Delhi’s air pollution crisis is complex and persistent. This underscores the need for long-term, systemic solutions rather than temporary fixes like water sprinkling, costly smoke towers, or cloud-seeding experiments. The only viable path is to tackle the root cause — source emissions. While implementation is challenging, the sooner Delhi adopts an airshed-based approach, the better it will be for the health and well-being of its residents. For effective AQ-management, the vision of NARFI (National Air Quality Resource Framework of India) prepared by NIAS needs to be realised to fill a long-standing void and achieve atmanirbharta.
The writer is chair professor, National Institute of Advanced Studies, IISC campus and founder project director, SAFAR
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