Kolkata Air quality today

Why is the air worst in winter?

The October to February months are when pollution typically peaks in Kolkata ^[3]. Kolkata sits at the eastern end of the Indo-Gangetic Plain, one of the largest, most populated and most polluted river basins in the world ^[5]. A 2020 study of October to December 2016 found that, towards winter, cooler air, weaker winds and a much shallower layer of mixing air leave pollution trapped near the ground across the plain ^[6]. In November 2016, that layer was only about 250 to 350 m deep over the central and eastern plain ^[6].

The winds also turn around. In summer they blow mostly from the south, off the Bay of Bengal, and bring cleaner air ^[5]. In winter they blow from the north and northwest, lining the city up with pollution sources upwind ^[5]. A 2025 report for the West Bengal Pollution Control Board says lower temperatures, more stable air and less vertical mixing in winter let pollutants build up near the ground ^[5].

Where does Kolkata's pollution come from?

The main concern is PM2.5, particles 2.5 micrometres across or smaller, which pose serious health risks, including breathing and heart problems ^[2]. A Bose Institute study of 2016 to 2023 data found that burning of biomass, such as wood and leaves, and solid waste is the key source making Kolkata's PM2.5 more toxic ^[2][3]. Vehicle exhaust also adds to the toxicity, though to a lesser extent ^[3].

The researchers point to the wide use of wood and other biomass as cooking fuel in poorer homes, and to burning dry leaves on winter mornings and evenings ^[3]. Road dust, building dust, vehicles and industry also add particles ^[2].

How bad does it get?

In winter 2025-26, from October to February, Kolkata's PM2.5 averaged 78 µg/m³ ^[1]. That is about twice India's national standard of 40 µg/m³ and about 16 times the World Health Organization's guideline of 5 µg/m³ ^[1]. Among India's biggest cities, Delhi averaged 163, Mumbai 48, Chennai 44 and Bengaluru 39 ^[1].

The Bose Institute found that PM2.5 grows sharply more toxic once it passes about 70 µg/m³, until about 130 µg/m³ ^[2]. From 2016 to 2023, the air in Kolkata's metropolitan area went past 70 µg/m³ on nearly 75% of days from October to February ^[3].

There are signs of progress. The Centre for Science and Environment found a winter average of 65 µg/m³ from October 2024 to January 2025, Kolkata's lowest in four years ^[4]. The worst day was 135 µg/m³ on November 2, 2024, and one area, Ballygunge, had a daily spike of 195 µg/m³ that winter ^[4].

What is being done about it?

Kolkata is one of 131 cities in India's National Clean Air Programme, launched in 2019 for cities that do not meet the national air standards ^[2]. The programme aims to cut particle pollution by 40% by 2026, compared with 2017 ^[2]. Kolkata used over Rs 636 crore from the programme between 2019 and 2023 ^[3].

The Bose Institute study found that emissions in the period after the programme began fell from vehicles by 33%, industry by 39% and road dust by 42% ^[3]. Burning of biomass showed no significant change ^[3]. The share of winter days above 70 µg/m³ fell from 80 to 85% before the programme to about 65 to 72% after it ^[3]. India's Department of Science and Technology said in 2025 that the study helped local bodies in Kolkata step up checks and action against biomass and waste burning ^[2].

How to protect yourself in Kolkata

When particle pollution is at unhealthy levels, US EPA advice is to take it easier outdoors: spend less time being active outside, and be active when the air is better ^[7]. Walkers, runners and cyclists can plan times and routes that avoid busy roads, and drivers can set the car's ventilation to recirculate on busy roads ^[7].

People with heart or lung disease, people with diabetes, older adults and children are among the groups US EPA lists as sensitive to particle pollution ^[7].