As firecracker ban in Delhi-NCR went up in Smoke during Diwali on Saturday evening, the average hourly PM 2.5 concentration reached 910 micrograms per cubic metre (g/m3) at midnight, 15 times the safe standard. Later it went down due to increase in wind speed.
The AQI touched ‘severe’ on Diwali with a reading of 414 as people flouted firecracker ban on Saturday. The AQI was recorded at 435 on Sunday, a Times of India report said.
Diwali this year has been worst since 2016 in terms of AQI as reading of 431 was recorded while it was recorded 445 the day after, data from Central Pollution Control Board and System of Air Quality showed.
The records for Diwali during the past year were comparatively low. The AQI was 337 on Diwali and 368 the next day in 2019; while it was 281 on Diwali day and 390 on the next day in 2018.
However, SAFAR had predicted the pollution level reaching ‘severe’ level the day after Diwali even if no firecrackers were burst.
The data of the CPCM showed that the pollution level was at the highest around midnight from 12 am to 1 am. "Diwali was in mid-November this year which has unfavourable meteorological conditions for dispersal of pollutants as compared to 2019 when it was in last week of October," it said. The contribution of stubble burning in Delhi's PM2.5 concentration was 32 per cent on Diwali day this year as compared to 19 per cent last year. "Therefore, it may be inferred that elevated PM2.5 concentrations in 2020 in comparison to previous year had enhanced contribution of stubble burning and the same is also reflected in elevated levels of CO and NO2," the apex pollution watchdog said.
“The surface temperature was at the lowest in past five years, which might have contributed to more inverse conditions and lowest average mixing height, which limits vertical dispersion. Wind speed and both pre-Diwali and Diwali day were similar. Overall, this Diwali witnessed higher backgrounds levels of pollutants and further addition of particulates during night from firecrackers,” CPCB added.
The spell of rain on Sunday afternoon not only helped in settling pollutants, but also increased wind speed Improving air quality.