NEW DELHI: Nine out of 11 state capitals analysed in India have recorded higher pollution in the first 12 hours after Diwali celebrations this year than what it was last year.

The government's National Clean Air Programme (NCAP) tracker analysed PM 2.5 (fine particulate matter) data for 11 capital cities--Bangalore, Bhopal, Chandigarh, Chennai, Delhi, Gandhinagar, Hyderabad, Lucknow, Mumbai and Patna--for the day before Diwali, the day of Diwali and the day after Diwali (till 12 pm) for the years 2022 and 2023.

The highest spike (recorded at 15-minute intervals) was seen in the national capital Delhi. It was at 999.5 ug/m3 at Pusa on November 13 at 1:30 am.

The NCAP Tracker is a joint project by Climate Trends and Respirer Living Sciences to create an online hub for the latest updates on India's clean air policy, the National Clean Air Programme (NCAP). The data was sourced from the Continuous Ambient Air Quality Monitoring Stations (CAAQMS) of the Central Pollution Control Board (CPCB)

Data analysis shows that a day before Diwali this year, eight of the 11 capital cities analysed - Bengaluru, Bhopal, Chandigarh, Chennai, Delhi, Hyderabad, Lucknow and Mumbai- had lower PM 2.5 levels as compared to October 23, the day before Diwali in the year 2022.

Except for Bangalore and Gandhinagar, all 11 cities recorded a dip in air quality after Diwali as compared to the previous year.

As per the data, "Post-Diwali pollution levels higher for 9 out of 11 capital cities in 2023 as compared to 2022.

Unseasonal rain ahead of Diwali made the high pollution levels of several capital cities such as Delhi, Mumbai and Chennai settle just ahead of the festival. But the Supreme Court's firecracker ban was flouted in many places, and air pollution started to spike on the night of November 12 and touched hazardous levels in quite a few places".

In the national capital, the pollution level on and before Diwali was lower than the previous years. As per the data, daily average PM 2.5 levels were 93.1 ug/m3 and 143. 8 ug/m3 a day before and on Diwali, respectively, as compared to 120.9 ug/m3 and 180. 9 ug/m3 last year.

However, data shows that after Diwali there was a sudden spike in the pollution level, as daily average PM 2.5 levels (12 pm) were recorded at 395.9 ug/m3 as compared to 166 ug/m3 in 2022.

For the same days, Gandhinagar, Kolkata and Patna had higher air pollution levels in 2023 than in 2022.

Firecrackers were burst in the national capital and other cities on Diwali despite alarming pollution levels and the Supreme Court's ban on bursting crackers.

Post-Diwali, Delhi-NCR's air quality significantly deteriorated and fell into the 'Poor' category, according to the Central Pollution Control Board (CPCB).