Chennai’s average PM10 level fell from 66 micrograms per cubic metre in 2017-18 to 58 in 2024-25, a 12% drop, according to Union government figures under the National Clean Air Programme (NCAP), reported by PTI. That makes Chennai one of the cleaner large metros on coarse dust, but the city still has a clear seasonal pattern: air is usually cleanest in the monsoon-fed summer winds and worst between late October and January.
This piece looks at the long-run numbers and the yearly cycle, using the official PM10 series, Tamil Nadu Pollution Control Board (TNPCB) daily bulletins and an analysis of CPCB station data by the Centre for Science and Environment. It does not cover live AQI or festival spikes, which change by the hour.
The long-run trend: PM10 under NCAP
NCAP tracks each city’s annual average PM10, the coarse particles from road dust, construction and combustion, against a 2017-18 baseline. Chennai’s figures, from a Lok Sabha answer of 2 December 2024 and the 2025 update:
| Year | Chennai PM10 (annual average, µg/m³) | Change from baseline |
|---|---|---|
| 2017-18 | 66 | Baseline |
| 2023-24 | 63 | About 5% lower |
| 2024-25 | 58 | 12% lower |
For comparison, the same 2025 update put Delhi at 203 (down 15% from 241), Kolkata at 92 (down 37% from 147) and Mumbai at 90 (down 44% from 161). Chennai started low, which partly explains its smaller percentage gain: sea breezes and a coastal location flush pollutants out more readily than in the Indo-Gangetic plain.
The yearly cycle: why winter is worst
Chennai’s air follows the winds. From roughly March to September, southerly and south-westerly winds and the daily sea breeze keep pollution moving. As the northeast monsoon sets in and winter arrives, winds weaken, mornings are calmer and a shallow layer of cool air near the ground traps smoke and dust. Festival fireworks and the Bhogi bonfires fall in this window too.
The CSE’s winter analysis of CPCB monitoring data, covering 1 October 2024 to 31 January 2025, put numbers to that season:
- Average PM2.5 over the winter: 36 µg/m³, about 1.2% above the average of the previous three winters.
- Peak daily city-wide PM2.5: 119 µg/m³ on 31 October 2024, around 19% lower than earlier winter peaks.
- Highest single-station peak: Velachery, at 193 µg/m³.
- Most “poor” or “very poor” AQI days at one station: Alandur, with 14.
- Arumbakkam, Royapuram and Perungudi saw winter levels more than 35% above their own annual averages.
So even though Chennai’s annual numbers are modest, a resident near a busy junction can see several bad-air days in a single winter.
What a clean month looks like
TNPCB publishes a daily AQI sheet for its continuous monitoring stations. Two sheets from May 2024 show how clean summer air can be. On 7 May 2024, Chennai stations read:
| Station | AQI, 7 May 2024 | AQI, 20 May 2024 | Main pollutant |
|---|---|---|---|
| Kodungaiyur | 42 | 12 | PM10 |
| Koyambedu | 52 | 19 | PM10 |
| Perungudi | 50 | 27 | PM10 |
| Royapuram | 40 | 15 | PM10 |
| Manali | 35 | 50 | PM2.5 |
All but one reading on those days fell in the “good” band (0 to 50). The 20 May sheet also shows the typical split in the city’s pollution: PM10, mostly dust, dominates at traffic and residential sites, while industrial Manali more often reports PM2.5, the finer particles from combustion.
Which pollutants matter most
Across the official sources, two pollutants drive Chennai’s AQI on most days:
- PM10: road dust, construction, metro and flyover works, unpaved shoulders. It is the pollutant NCAP targets and the one most often named in TNPCB bulletins.
- PM2.5: vehicle exhaust, burning waste, industry in the north (Manali, Ennore), and festival smoke. These particles penetrate deeper into the lungs and dominate the winter peaks CSE recorded.
The TNPCB sheets also show gaps: Kathivakkam reported no data on either May day, and Kuruchi-SIDCO’s row was blank on 20 May. Missing readings are common, so a city-wide average on any day may rest on fewer stations than the list suggests.
Gaseous pollutants such as nitrogen dioxide are measured too, but rarely appear as the lead pollutant in Chennai’s published sheets.
Quick answers
Is Chennai’s air getting better?
On PM10, yes. The annual average fell from 66 µg/m³ in 2017-18 to 58 in 2024-25 under NCAP.
When is Chennai’s air worst?
Late October to January, when winds are weak and festival smoke adds to traffic and dust. The 2024-25 winter peak was on 31 October.
Which area had the worst air last winter?
Velachery recorded the highest daily PM2.5 peak (193 µg/m³) and Alandur the most poor-AQI days (14), per CSE’s analysis.
Where can I see daily figures?
TNPCB posts daily AQI sheets on tnpcb.gov.in, and CPCB’s national AQI portal shows live readings. People with asthma or heart conditions should follow their doctor’s advice on bad-air days.
Information checked against official sources on 18 October 2026. Fees, dates and rules can change; confirm on the linked official pages before acting.
Sources
- Lok Sabha Unstarred Question No. 1077, 2 December 2024, NCAP city PM10 levels (Ministry of Environment, Forest and Climate Change)
- Mumbai logs highest decline in PM10 level in 2024 among metros covered under NCAP: Govt (PTI via The Week, July 2025)
- Winter pollution crisis in megacities of India: going beyond Delhi, Chennai (Centre for Science and Environment, March 2025)
- Air Quality Index of 34 CAAQM stations, 7 May 2024 (Tamil Nadu Pollution Control Board)
- Air Quality Index of 34 CAAQM stations, 20 May 2024 (Tamil Nadu Pollution Control Board)
