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........

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