The pollution crisis: How our cities struggle to breathe

Delhi is the worst case. But clean air is rare in other cities too. The data reported in this story reveal stark seasonal and regional differences across six Indian metros.

In Short

• Poor-or-worse conditions covered 771 reported days in Delhi since 2022
• November consistently brought worst air, while monsoon months offered relief
• Mumbai recorded no poor or worse days through November 4 in 2026

Imagine a child born in Delhi on Jan 1, 2022. Think of their first laugh, the first steps, the first words. In the 1,769 days they have been on Earth, the air in their birthplace was "Good" on a total of "five" days, according to the Central Pollution Control Board's (CPCB) daily air quality bulletin.

For 771 days, Delhi's air was "Poor" or worse, a count of the bulletins by the Data Intelligence Unit (DIU), India Today's data team, shows. That is 43.6 per cent of the days the board reported. Air this bad "may cause breathing discomfort to people on prolonged exposure," says CPCB's 2014 report on the National Air Quality Index.

On 293 days, the air was "Very Poor". That level "may cause respiratory illness in people on prolonged exposure," the report says. For 48 days, it was "Severe", the band that "may cause respiratory effects even on healthy people".

The days in between brought little relief. For another 660 days, the air was "Moderate". Moderate air may bring discomfort to "people with heart disease, children and older adults," the same report warns. Add them up: 1,431 of the child's days were moderate or worse. That is 80.9 per cent.

WHAT THE AIR DOES

The harm does not stop at a sore throat. Specks too small to see can help clots form in the blood, reporting on Delhi's air in 2020 found. A clot can bring on a heart attack. The specks can hurt the liver and the brain too. Some hold poisons, among them arsenic and lead.

A medical study tied about 15 lakh extra deaths a year in India to years of dirty air. It came out in December 2024. It compared India's air from 2009 to 2019 with air that met the World Health Organisation's (WHO) guideline. "Every 10 microgram per cubic meter increase in PM2.5 concentration led to an 8.6 percent increase in mortality," Joel Schwartz, a co-author at the Harvard TH Chan School of Public Health, said. The rise was even larger below India's own standard of 40 micrograms, he added.

Delhi is the worst case. But clean air is rare in other cities too. The board's bulletins rated 335 cities on at least one day since Jan 1, 2022. They show that some metros breathe far cleaner air than others. In most of them, a Good day comes with a season, and leaves with it.

DELHI'S WINTER WALL

Delhi's bad air has many sources, and no one step will fix it. Its timing, though, barely changes. Each autumn and winter, cold, still air holds the pollution low over north India. The Himalayas, to the north, stop it from blowing away, the same 2020 reporting found.

The board's own numbers show the pattern. November is Delhi's worst month. Every November day the board reported since 2022 was Poor or worse. In each November from 2022 to 2025, the air was "Very Poor" on average.

Relief comes in July and August. In both months, Delhi's air quality index (AQI) was 93 on average, in the "Satisfactory" band. Yet even then, Good days were rare. In five years there were two in September, two in October and one in July.

There is some easing. From Jan 1 to Nov 4, Delhi had 148 Poor-or-worse days in 2022. In 2026, it had 89 over the same stretch. That is the fewest of the five years. But the count stops before the worst weeks of the year.

MUMBAI'S CLEARER YEARS

Mumbai changed even more. From Jan 1 to Nov 4, it had 21 Good days in 2022 and five in 2023, the bulletins show. Over the same stretch, it had 82 in 2024, 55 in 2025 and 87 in 2026.

Its bad days almost vanished. Mumbai had 23 Poor-or-worse days in 2022 and 34 in 2023, from Jan 1 to Nov 4. It had one each in 2024 and 2025, and none in 2026.

The chart shows where the gain came. From June to September 2026, Mumbai had 72 of its 87 Good days. August alone had 27.

WHEN THE AIR CLEARS

In most metros, Good days arrive in the same months. In Kolkata, 81.9 per cent of July days were Good, the bulletins show. In Mumbai, 50.3 per cent of August days were Good. Hyderabad and Bengaluru had the most Good days in July.

Kolkata had the most Good days of the six: 460, or 26 per cent of the days reported. It also had 197 Poor-or-worse days. Almost all came between November and February. In January, 55.8 per cent of Kolkata's days were Poor or worse.

Chennai keeps a different calendar. Its most Good days came in April: 61 days across five Aprils, or 40.7 per cent.

Bengaluru and Hyderabad did not have one Poor-or-worse day in five years. But Good days were few: 225 in Bengaluru and 132 in Hyderabad. Most days were "Satisfactory": 1,263 in Bengaluru and 1,315 in Hyderabad. Satisfactory air "may cause minor breathing discomfort to sensitive people", in CPCB's words.

WHAT THE AIR COSTS: YEARS OF LIFE

Polluted air shortens lives. That is the finding behind the Air Quality Life Index (AQLI). It comes from the Energy Policy Institute at the University of Chicago. Its 2025 update uses satellite data for 2023.

India's average fine-particle pollution (PM2.5) was 41 micrograms in each cubic metre of air (g/m) that year, according to AQLI. That is about eight times the WHO's guideline of 5 g/m.

That guideline is the WHO's limit for the air people breathe over a year. On average, each cubic metre of air should hold no more than 5 micrograms of fine particles. Every one of India's 140 crore people lives where the air is dirtier than that. Even Leh, the cleanest district, is just above it.

If India met that guideline for good, the average Indian could live 3.5 years longer. In Delhi, the gain would be 8.2 years, the most of any district in AQLI's data. Next come Noida's district, Gautam Buddha Nagar, and Ghaziabad, at 7.7 years each. Then Gurugram, at 7.1, and Faridabad, at 6.8.

India's own standard is looser, at 40 g/m. Even so, 234 of the 690 districts in AQLI's data were above it. Those districts are home to 46 per cent of Indians.

If those districts met India's own standard, their people could live about 1.5 years longer on average. In Delhi, meeting even that looser standard would add 4.7 years.

The worst air is in the northern plains: Bihar, Chandigarh, Delhi, Haryana, Punjab, Uttar Pradesh and West Bengal. About 54.5 crore people live there, 39 per cent of Indians. They could gain about five years of life. Bihar's people could gain 5.4 years, Haryana's 5.3 and Uttar Pradesh's five.

AQLI works these figures out from the data. They are not counts of deaths. AQLI bases them on studies of a heating policy in China. Each extra 10 g/m of PM2.5, breathed for a lifetime, cuts 0.98 years off a person's life, by its method. Its yearly satellite figure is also not the daily index CPCB publishes. The two measure the air in different ways.

Not every study finds an effect that large. A 2009 study of US cities found a smaller gain. There, a 10 g/m cut in PM2.5 went with 0.61 more years of life. A result from China or the US may not fit India. In 2020, there was little research on long-term harm where the air is as dirty as India's, as noted in reporting from that year. The 2024 study of deaths across India is one such study. AQLI's figures show the size of the harm, not an exact count.

BEFORE THE CHILD TURNS FIVE

The child from the start of this story turns five on Jan 1, 2027. In that time, Delhi's air has been "Good" on five days, the bulletins show. The last came on July 9, 2026, after a wait of 1,033 days.

Next come the city's worst weeks. In each of the last four years, Delhi's November air was "Very Poor" on average. All five "Good" days fell between July and October. If the past five years are a guide, the child's sixth "Good Day" is at least eight months away.

- Ends