According to WHO guidelines, the daily concentration of ozone should not exceed the 100-mark but Bidhannagar's 24-hour average was 160.
The heatwave conditions in the southern West Bengal districts will continue for the next four days, the weather office warned on Monday. Bankura recorded the highest temperature in the state at 43.7 degrees Celsius, while Kolkata's maximum was 40 degrees Celsius, it said.
The weather office warned that heatwave conditions will continue to prevail in Gangetic West Bengal for the next four days. Stating that mainly dry westerly wind is prevailing over the region, it said that meteorological conditions suggest no large change in maximum temperatures till April 21.
Heatwave conditions were recorded in Bankura (43.7), Sriniketan (43.2), Panagarh (43), Dum Dum (41.6 degrees Celsius), Uluberia (40), Diamond Harbour (39), Contai (40.6) and Krishnanagar (41), among other places. Amid the heatwave, the ground-level ozone reached an alarming 160 in Bidhannagar in North 24 Parganas district, a West Bengal Pollution Control Board official said.
Ozone production accelerates at high temperatures, and emissions of the natural components of ozone increase as weak winds cause the atmosphere to stagnate, he said. The Air Quality Index (AQI) was 100 (moderate) at Bidhannagar during the day, he said, adding that ozone was the prominent pollutant.
At Rabindra Bharati University in north Kolkata, the AQI was 151 (unhealthy), while in Ballygunge in south Kolkata, it was 127 (unhealthy). Ozone, which is formed when nitrogen oxide and volatile organic compounds react with each other in sunlight, causes respiratory problems. It is caused by vehicular and industrial emissions, among others, leading to the creation of smog, the official said.
Environmentalist SM Ghosh said if the ozone level is within 50, it is not harmful for people staying outside. According to WHO guidelines, the daily concentration of ozone should not exceed the 100-mark but Bidhannagar's 24-hour average was 160, he said.
As declared by the state government, schools, colleges and universities were closed across the state, except in the two hill districts of Darjeeling and Kalimpong. Some private schools switched to online classes.
The centrally-funded Visva-Bharati in Birbhum declared a holiday for students in kindergarten to standard 8. The classes for students in standards 8 to 12 will be held from 6.30 am to 9.30 am. Classes for all undergraduate and post-graduate courses will be held from 7 am to 11 am, it said in a notification. Fewer people were out on the streets and lesser public transport was available owing to the high day temperatures and oppressive heat.