An analysis of air quality data since 2015 shows that the average air quality index (AQI) worsens by 16% in the four days following Diwali compared with the four days preceding it. New Delhi: If history is any guide, Delhi-NCR’s air quality is likely to deteriorate sharply in the coming days. The number of severe air days also triples in the post-festival period.
In 10 of the 11 years since air quality monitoring began in Delhi, post-Diwali AQI readings were higher than pre-Diwali levels, underlining the recurring impact of fireworks and associated emissions. In eight of these years, the difference exceeded 10%, crossing 30% in four years. Last year, the average AQI increased by 10% in the four days following Diwali. The reading rose from 345 on the festival day to 351 the next day and 353 on the day after. TOI had reported that a majority of air quality monitoring stations in the city stopped transmitting data during peak pollution hours on Diwali night, when AQI had maxed out at 500.
This pulled down the average recorded for the day after.
Since 2015, Delhi has recorded 15 severe air days in the four-day period after Diwali, compared with five in the four days leading up to the festival. The pattern was repeated in 2021, when the average AQI climbed from 320 to 429, an increase of 34%. Significant rises were also recorded in 2018 and 2019, when post-Diwali pollution levels were 33% and 31% higher, respectively.
This is despite the fact that pollution levels typically rise even before Diwali, driven largely by increased traffic and congestion.
The only exception was 2020, when the average AQI fell by 26% in the four days after Diwali. It actually peaked at 435, in the severe category, the day after Diwali, compared with 414 on the festival day. Rainfall across several parts of the region subsequently brought readings down to 221, 171 and 211 over the next three days. Under Central Pollution Control Board’s system, the 24-hour average up to 4pm is taken as the day’s AQI.
But the improvement had little to do with any restraint in firecracker use. Consequently, pollution from Diwali night and the following morning is reflected in the next day’s reading. Environmental experts have repeatedly warned that firecracker emissions coincide with unfavourable meteorological conditions typical of north India in late autumn. Falling temperatures, low wind speeds and atmospheric stagnation trap pollutants close to the ground, amplifying the impact of festive emissions.