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Delhi’s overall Air Quality Index was 462 on Friday, deep in the severe zone. This was the worst AQI the city has seen the day after Diwali since monitoring began in 2015. Delhi also recorded the sharpest deterioration in AQI since 2015, from the day before Diwali (AQI 314 ) to the day after.
The widespread flouting of the Supreme Court order banning firecrackers added to other factors, creating a “perfect storm” of dirty air over the region. The wind direction and low wind speeds facilitated the transport of farm fire pollutants from neighbouring states. The share of pollution from stubble-burning in Delhi’s AQI rose from 25% on Thursday to 36% on Friday, the highest so far this season.
Delhi also recorded moderate fog on Friday morning as visibility dropped to 200 metre in Safdarjung and 350 metre at Palam, conditions that made the air worse. Finally, low temperatures – with the minimum at 15 degrees Celsius – trapped pollutants close to the land surface, experts said.
On Thursday, the AQI went from “very poor” at 4pm to “severe” (414) by 10 pm. SAFAR, a pollution monitoring body under the Union ministry of earth sciences, said, “Firework emissions on the night of Diwali degraded the air quality from ‘very poor’ to ‘severe’ category.”
Calm after Diwali storm to blame for ‘severe’ air
In terms of AQI, this was the worst post-Diwali day since the Central Pollution Control Board (CPCB) started measuring AQI. Before this, the highest AQI on post-Diwali day was recorded at 445 in 2016. The AQI on Diwali day this year was better than in 2020 but worse than the 2019 level. Last year too, a complete ban on firecracker was flouted, with the AQI deteriorating from 330 (very poor) on pre-Diwali day to 414 (severe) on the day of the festival. The AQI on Diwali day in 2019 was 337 (very poor).
The CPCB central control room data showed that Delhi-NCR’s average 24-hour PM10 and PM2.5 concentrations were both in the “severe” category of Graded Response Action Plan as these crossed 500 and 300 micrograms per cubic metre for over 14 and 20 hours, respectively. The 24-hour average PM10 was 545.3 micrograms per cubic metre and the PM2.5 was 425.5 micrograms per cubic metre. The standard PM10 and PM2.5 is 100 and 60 micrograms per cubic metre, respectively.
“The sudden deterioration this year is attributed to extremely calm conditions, change of wind direction, low ventilation coefficient and use of firecrackers. Though the increase in trend in the concentration of pollutants like PM2.5 and PM10 was observed since the evening of November 3, the major changes were observed after 8pm on Diwali, when the fireworks started. Ambient Air Quality in Delhi was already in the ‘very poor’ category due to the accumulation of pollutants in the air shed,” said Delhi Pollution Control Committee.
Anumita Roychowdhury, executive director research and advocacy, Centre for Science and Environment, said, “The season’s first severe smog episode was observed when all factors – unfavourable weather conditions, increased share of biomass burning and use of firecrackers -came into play.”
However, the India Meteorological Department (IMD) has predicted strong winds at the speed of 25-35kmph during the day on Saturday and Sunday, the air quality is likely to improve. SAFAR said on Friday, “Local winds have picked up since morning and now the fast dispersion is expected. Without any more firecracker emissions, AQI is likely to improve to ‘very poor’ category by tonight although the stubble contribution is expected to remain almost the same as today. Relief is expected only from the evening of November 7 but AQI will fluctuate within the “very poor” range.”
Watch Cracker ban fail: Delhi AQI poorest ever post-Diwali