In Mumbai, a coastal city that once relied on sweeping sea breezes to clear its skies, winter pollution has become an inescapable feature of its urban environment. A dive into the air quality index (AQI) data across the past five winters makes it clear that clean air in Mumbai has practically vanished, and the city has normalised chronic exposure to polluted air.

Sample some of these concerning data points.

Over the last five winters (October to February) between 2021 and 2026, the city recorded 7 days of ‘good’ air (daily average AQI less than 50), according to Central Pollution Control Board (CPCB) data. Most notably, 6 of those days occurred during the 2025–26 season in October and November, with only a single ‘good’ day recorded in the four years prior.

The data also shows a sustained dominance of ‘moderate’ AQI days (101-200). In December 2024 and January 2025, for example, Mumbai recorded exactly 31 ‘moderate’ days each. For two consecutive months, residents did not breathe a single day of ‘good’ or ‘satisfactory’ (51-100) air. The story was nearly identical in 2023–24, where 29 days in October, 31 in December, and 27 in January fell into the ‘moderate’ category. Even in 2025-26, between December and February, the city saw only 8 days when the AQI fell below 101.

Looking at the particulate matter data, notably for PM2.5 and PM10 between 2022 and 2026, the figures don't make for pretty reading.

According to CPCB data, approximately 45 percent of winter days exceeded India's National Ambient Air Quality Standards, which set a 24-hour average exposure limit of 60 µg/m³ for PM2.5. Applying the WHO's more stringent 24-hour average exposure limit of 15 µg/m³ for PM2.5 — which the global body recommends should not exceed more than 3-4 days per year — a staggering 99.3 percent of winter days exceeded this threshold. The situation for PM10 is even more dire: over 82 percent of days failed to meet the national standard of 100 µg/m³, while nearly 98 percent exceeded the WHO's global safety limits.

The yawning gap between the two benchmarks is worth interrogating in its own right. Dr Abhishek Chakraborty, Assistant Professor at IIT-Bombay's Environmental Science and Engineering Department, in conversation with Newslaundry, notes that “it is not entirely clear to the scientific community how the WHO arrived at its figures,” adding that “being a tropical country, naturally high dust levels and intense photochemistry driven by high solar radiation” justify a different standard than cooler nations.

He does, however, acknowledge that India's current limits are “among the most relaxed in the world,” and proposes a gradual tightening to 30–40 µg/m³ as a meaningful middle ground. “As long as the standards remain as they are,” he warns, “industry and regulatory agencies have little motivation to push for further reductions.”

Why October's clarity is fleeting

Across the last five years, CPCB Air Quality Index data from October to February follows a recurring pattern. Each year, October is a transitional month, typically hovering near the satisfactory baseline (51-100), with averages of 96 in 2021-22, 95.7 in 2022-23, 84.2 in 2024-25, and 95.74 in 2025-26. However, AQI levels rise sharply and remain dangerously elevated through November, December, and January. By February, the city sees a slight improvement, but the air never returns to its pre-winter clarity.

The winter peaks have been well documented, but the most alarming trend is the near-extinction of clean air days categorised as ‘good’ with an AQI between 0 and 50. In the entire winter of 2023–24, Mumbai did not record a single ‘good’ air day from October to February. In 2024–25, the city managed exactly one ‘good’ air day in October, before they disappeared completely. Even in the 2025–26 cycle, we saw a brief respite of six ‘good’ days.

During the winter of 2022-2023, the average AQI crossed into the ‘poor’ range (201-300) for months, hitting an average of 202 in December and 202.9 in January. December and January each saw 17 ‘poor’ days (AQI 201-300), followed by 12 more in February. The years following that extreme peak show the city stabilising into a persistently unhealthy equilibrium. The extreme peaks have become less frequent; the 2025-26 season saw no ‘poor’ days, but the unhealthy AQI baseline of 101-200 (‘moderate’) remains untouched.

A marginal improvement, but not cause for relief

Recent data suggests a gradual decline in pollution severity. The recent winter season, from October 2025 to February 2026, recorded the fewest unhealthy days for PM2.5 (above 60 µg/m³) and PM10 (above 100 µg/m³) in the last four years.

But Dr Abhishek Chakraborty warns against reading too much into a single-season improvement. “For now, I would treat this as a good start,” he told Newslaundry, explaining that a single year's data is statistically and scientifically insufficient to make sweeping statements and may very well be an outcome of “favourable weather patterns” rather than successful policy interventions. “As for whether Mumbaikars can take comfort from it — I would need another five years of data before I could answer that with any confidence.”

The numbers bear out his caution. In October alone, PM2.5 levels surged to 98.60 µg/m³ and PM10 reached 183.19 µg/m³. Across the full 146 days, 33 exceeded the national PM2.5 limit and 75.3 percent breached the PM10 benchmark, meaning a significant chunk of the winter failed even India's domestic standards. 

What explains Mumbai's descent into polluted air

Dr Chakraborty describes the problem as “a confluence of factors — congestion, construction, increasingly active atmospheric chemistry, and a climate-change-driven weakening of the sea breeze, though more conclusive evidence is yet to emerge”. Mumbai is possibly losing the coastal advantage that once diluted its pollution woes, slipping into a troubling winter AQI baseline of 101-200.

Beyond Dr Chakraborty’s observations, it is important to note that natural defence mechanisms have been destroyed. Vast stretches of mangroves and parts of the Aarey forest have been sacrificed for infrastructure, amplifying the Urban Heat Island effect and disrupting local micro-winds that naturally help disperse ground-level pollutants. Without these winds, particulate matter lingers in the air far longer.

On the specific question of soaring PM10 levels, Dr Chakraborty attributes "much of the increase” to “construction dust,” with the remainder tied to “changing climate patterns.”

“Rising temperatures and slightly higher surface wind speeds mean that dust particles tend to stay airborne for longer,” he explained, noting that warmer, more turbulent conditions make it far easier for particles to remain suspended in the atmosphere.

What’s more, the pollution burden is not evenly distributed across the city. An analysis by the Centre for Science and Environment's (CSE) Urban Lab for the winter of 2024-25 shows Mumbai's air pollution is intensely localised — neighbourhoods just a few kilometres apart breathe very different air. According to their analysis, while the citywide winter PM2.5 average was 50 µg/m³ (Mumbai's lowest in four years), certain hotspots suffer dramatically worse conditions. Industrial areas like Mahul and Dharavi, which are also home to scores of low-income families, register choking concentrations of SO₂ and PM10, driven by smelting, oil burning, and coal combustion. Right next to the massive Deonar dumping ground, Deonar recorded a winter PM2.5 average of 80 µg/m³. Shivaji Nagar followed closely at 76 µg/m³. In these hotspots, pollution levels are up to 60 percent higher than the citywide baseline.

What will it take to fix this?

Dr Chakraborty is clear that there are no quick wins. On construction dust – the dominant driver of PM10 — he suggests targeted interventions: “applying dust-suppressing compounds to construction sites, which reduces the re-suspension of dust particles,” and focusing controls specifically on “the most dust-intensive activities — drilling and excavation.” 

He also argues for smarter planning at the government level. “The government should think about prioritising and phasing construction activity. Which projects are urgent, and which can be delayed? Could construction in a given zone be restricted to certain days or times, so that dust from multiple sites does not accumulate in the atmosphere simultaneously?”

On vehicular emissions, he sees promise in technology-driven enforcement. “One practical tool already available is IR-thermal cameras at traffic junctions, which can capture the emission plumes of passing vehicles. These could be integrated with a digital system that cross-references a vehicle's number plate with its Pollution Under Control (PUC) certificate.” 

If a vehicle's plume indicates elevated emissions but its recently uploaded PUC certificate claims otherwise, both the vehicle owner and certifying operator can be automatically held accountable. “This kind of AI-assisted digital enforcement would remove the need for manual checks and would significantly reduce the existing issues in the current PUC system.”

In the long term, he argues, Mumbai must be fundamentally decongested. “No amount of new metro lines or roads will solve the problem if the number of vehicles continues to increase rapidly.” He points to models such as Singapore-style limits on vehicle ownership, congestion pricing, or pollution surcharges, as implemented in Paris — but insists these only work if public transport becomes “a genuinely attractive alternative: frequent, comfortable, and clean.”

Finally, he flags solid waste management as a seriously underappreciated source of pollution in Mumbai. The solution, he argues, “begins with citizens.” He states, “Waste must be segregated at source, and must be backed by financial penalties for non-compliance.” He also adds, “governments must invest in proper infrastructure, phasing out open landfills in favour of controlled incineration and well-designed, sustainable waste-to-energy facilities.”

“If Mumbai can make meaningful progress on decongestion, transition to EVs powered by clean energy, raise public awareness, enforce compliance rigorously, and root out issues in the PUC system,” Dr Chakraborty concludes, “there is every reason to expect significant air quality improvements within five years.”

With inputs from Hasi Jain.

This show is part of a collaborative campaign to tackle air pollution. Here’s how you can join the Fight To Breathe. Click here to power this campaign.

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