On Deepavali night last year, 20 October 2025, the CPCB monitor at Velachery hit an AQI of 401, the worst band on India’s scale, while Perungudi touched 331 and several other Chennai stations crossed 250 (DT Next). By the next morning the readings had fallen back to between about 130 and 200.
Deepavali falls on 8 November this year (DT Next), and Bhogi follows in mid-January. Both reliably push Chennai’s air into the red for a night or two. Here is how to check the numbers yourself and what they mean for your family.
Where to check Chennai’s AQI
The Central Pollution Control Board runs the National Air Quality Index portal. Choose Tamil Nadu as the state and Chennai as the city to see each continuous monitoring station, its current AQI, the main pollutant driving it, and minimum, average and maximum values over recent hours. You can also compare cities.
The Tamil Nadu Pollution Control Board operates monitoring stations in the city and runs special monitoring around Bhogi and Deepavali. Readings from the stations closest to you, such as Velachery, Perungudi, Arumbakkam, Kolathur or Manali, tell you more than a single city average.
A few tips for reading the portal:
- Look at the time stamp. Readings are updated through the day and can lag.
- Check which pollutant is “prominent”. After fireworks it is usually fine particulate matter.
- “Insufficient data” means a station did not report enough readings, not that the air is clean.
What the numbers mean
India’s National AQI was launched in October 2014 and is built from up to eight pollutants: PM10, PM2.5, nitrogen dioxide, sulphur dioxide, carbon monoxide, ozone, ammonia and lead. Each gets a sub-index, and the worst one sets the overall figure (PIB).
| AQI | Category | Likely health effect |
|---|---|---|
| 0-50 | Good | Minimal impact |
| 51-100 | Satisfactory | Minor breathing discomfort for sensitive people |
| 101-200 | Moderate | Discomfort for people with asthma, lung or heart disease, children and older adults |
| 201-300 | Poor | Breathing discomfort for most people on prolonged exposure |
| 301-400 | Very Poor | Respiratory illness on prolonged exposure |
| 401-500 | Severe | Affects healthy people; serious for those with existing disease |
The Deepavali spike
Last year’s spike began sharply after 7 pm on Deepavali. Tiruvanmiyur, Guindy, Kilpauk, Vyasarpadi and Manali all crossed 250, and smog cut visibility on some roads to under 50 metres. The Valasaravakkam station, for comparison, had recorded 287 on Deepavali in 2024 and 365 in 2023 (DT Next). The state permits fireworks only in two time slots on the day, though DT Next reported that enforcement was weak.
The pattern last year was worth noticing. The southern and suburban stations rose more sharply than in earlier years, and the haze reached into underground metro stations. Readings had eased to the Moderate and Poor bands by the next morning, with Perungudi at 197, Arumbakkam 149, Velachery 148 and Kolathur 128. So the worst stretch is the evening and night of the festival itself, which is when to keep vulnerable family members indoors.
Spikes are not limited to festivals. Around the same time last year, DT Next reported a Tamil Nadu study finding that Chennai’s AQI readings were the worst in the state and that pollution at times exceeded national standards. Readings differ a lot between neighbourhoods, which is why the station nearest your home is the number to watch.
Bhogi bonfires
Bhogi bonfires on the morning before Pongal cause a different kind of smog, heavier at dawn. This January it was described as mild and short-lived in many areas. Domestic flights ran normally, though a few international arrivals were slightly delayed. TNPCB, which has campaigned for an eco-friendly Bhogi for 21 years, again asked people not to burn tyres or plastic (DT Next/PTI).
Protecting yourself on bad-air days
- Check the station nearest you before morning walks; postpone exercise outdoors if it is Poor or worse.
- Keep windows shut on Deepavali night and Bhogi morning, and air the house once readings drop.
- Keep children, older relatives and anyone with asthma indoors during peaks, with inhalers handy.
- A well-fitted N95-type mask helps more than a cloth mask if you must go out.
- Two-wheeler riders on arterial roads such as the Velachery Main Road or OMR get the heaviest dose; leave earlier or later if you can.
Quick answers
How do I check AQI in my area of Chennai?
Open the CPCB AQI portal, choose Tamil Nadu and Chennai, and pick the nearest station.
What AQI is unsafe?
Above 100 can affect sensitive people. Above 200 is Poor, and most people feel effects with long exposure.
When is Deepavali 2026?
Sunday, 8 November 2026.
Why is Velachery often worst?
Last year it recorded the highest Deepavali reading in the city, 401, though readings vary year to year by station.
If you have asthma, COPD or heart disease, consult your doctor about a plan for festival 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
- Environment Minister launches National Air Quality Index, 2014 (PIB)
- National Air Quality Index portal (CPCB)
- Tamil Nadu Pollution Control Board
- Chennai wakes up to smog and poor visibility as post-Deepavali pollution peaks (DT Next)
- TN celebrates Bhogi with bonfires leading to mild smog (DT Next / PTI)
- TNSTC Deepavali 2026 bus booking explainer (DT Next)
