It was recorded at 317 microgram per cubic metre on November 17, which is three times the normal.

People exposed to “very poor” air for a prolonged time can develop respiratory illness.

The air quality index (AQI) is recorded on alternate days at five centres in the city. The Chandigarh Pollution Control Committee released the figures for the November 17 readings on Monday.

At two other locations, the air quality was “poor”, and “moderate” in the remaining two.

“The city witnessed light rain and wind, so ideally the air quality should have improved,” said DrRavindraKhaiwal, associate professor of environment at the School of Public Health, Post Graduate Institute of Medical Education and Research (PGIMER). “However, if the AQI is still so high, there must be localised sources of pollutants. These must be investigated to better manage the air quality.”

Earlier, it was on November 9 that the AQI measured at the Industrial Area was “very poor”: 303 microgram per cubic metre. It had been varying between poor and moderate since then.

For instance, it was moderate (153) on November 11, then dipped to poor (240) on November 13. It again improved to moderate (123) on November 15 but worsened on November 17.

Also, the presence of particulate matter (PM) 2.5 was 142, which is more than double the normal limit of 60, and PM10 was 176, against the normal limit of 100.

Meanwhile, the air quality at the PEC University, Sector 12, and Sector 17 was “poor”, which can lead to breathing discomfort to people on prolonged exposure. The index was 243 at both the places. Earlier, on November 9, the air quality had dipped to “poor” at Sector 17.

At the other air quality monitoring stations – Institute of Microbial Technology (IMTECH), Sector 39, and Kaimbwala village — the air quality on November 18 was moderate. It can lead to breathing discomfort to diseased people.