Why was this Diwali in Delhi the cleanest in years?

The Delhi government’s ban on firecrackers was of little help on Monday, the day of Diwali, as many residents chose to defy the prohibition.

Opposition BJP and Congress on Tuesday hit out at the Aam Aadmi Party government, alleging it had failed to implement the ban.

To fight extreme winter pollution, Delhi government had in September announced a complete ban on the production, sale and use of all types of firecrackers till January 1, including on Diwali, a practice it has been following for the past two years.

Even as Delhiites flouted the ban with impunity on Diwali evening, they woke up to a pleasant surprise the next morning.

The dip in air quality wasn’t as bad as recent years.

The 24-hour average Air Quality Index at 4 pm on Tuesday stood at 303, the lowest for the day after Diwali since 2015, when the Central Pollution Control Board (CPCB) started maintaining air quality data.
 

On Monday, the city recorded an Air Quality Index, or AQI of 312, the second best for Diwali in seven years. The city had recorded an AQI of 281 on Diwali in 2018. 

An AQI between 301 and 400 still falls under the ‘very poor’ category and can cause respiratory illness on prolonged exposure.

The concentration of poisonous PM2.5 particulate matter was 15 times more than safe limits in the 24-hour period starting Monday, according to data from the Delhi Pollution Control Committee.
 

Last year, Delhi woke up to a blanket of smog, enveloping the city on the day after Diwali. Why was it different this time?

Gufran Beig, Founder Project Director, IITM-SAFAR says, change in wind direction was unfavourable for stubble smoke. Warmth, winds helped prevent the accumulation of pollutants. Winds did not become stagnant like usual the morning after Diwali. 

Delhi is the world’s most polluted capital and its air becomes particularly bad from mid-December to February as heavy, cold air traps dust, vehicle emissions and smoke from burning crop stubble in states like Punjab and Haryana.

Emissions from firecrackers and farm fires have contributed significantly to Delhi’s PM2.5 pollution on Diwali over the years.

The contribution of stubble burning to Delhi’s pollution on Diwali increased to around 10%, the highest this year so far, according to SAFAR, a forecasting agency under the Union Ministry of Earth Sciences. The share of farm-fires in Delhi’s PM2.5 pollution was 25% on Diwali in 2021, 32% in 2020 and 19% in 2019. 

Stubble burning in Haryana and Punjab peaks in October-end and November. While its contribution to air pollution on Diwali was not significant, it is likely to rise sharply in the upcoming days.

Since Diwali was observed early in the season this year, moderately warm and windier conditions prevented rapid accumulation of pollutants from firecrackers bursting and reduced the effect of stubble burning.

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Anumita Roychowdhury, Executive Director, Research and Advocacy, Centre for Science and Environment says, it’s a warmer Diwali, usual winter conditions yet to build up. Festival did not coincide with intense crop fire. Smog episodes occurring in later winter show pollution is high. 

And, certain factors were favourable this year. During winters, when Delhi experiences temperature inversion, cold air at the surface mixed with pollutants gets trapped under a layer of warmer air that acts as a lid. 

But an early Diwali, warm weather, windy conditions, a delay in withdrawal of monsoon, excessive October rains, a delayed paddy harvesting and in turn stubble burning meant that pollution did not get trapped near the ground. This led to relatively better air quality than previous years in the capital this Diwali.