Post-Diwali smog can aggravate winter pollution level in Delhi: CSE

Delhi pollution

New Delhi (NVI): Despite the much talked about ban on crackers in national capital, the concentrated bursting of crackers after 10 pm at night on Diwali had spiralled the pollution curve to nearly the same “severe” level that was observed during the previous Diwali in Delhi-NCR.

The Air Quality data of Centre for Science and Environment (CSE) indicates that this happened despite the 2019 Diwali being warmer and windier than in 2018. This temporarily undid the comparatively better air quality gains of this season due to favourable weather, on-going pollution control action and preventive emergency measures, said CSE in the statement.

Anumita Roychowdhury, executive director-research and advocacy of CSE said, “While harsher winter conditions are yet to set in and the weather during the period of analysis (September 15 to October 27) has remained relatively favourable (including a delayed monsoon), several ongoing systemic actions and preventive emergency measures had also contributed to prevent an early onset of very poor and severe pollution in Delhi-NCR. The scenario has changed on Diwali night.”


As we go deeper into winter, the occurrence of episodic smogs can upset and skew the overall winter pollution trend. This demands stronger and continuous action in Delhi and across NCR to reduce the overall pollution, she added.

“It is absolutely necessary that action is now stepped up to ensure that Delhi and NCR do not plunge into a prolonged smog episode this winter,” Roychowdhury said adding, “Enforce emergency action on industrial pollution, waste burning and dust generators with strong deterrence and zero tolerance across Delhi and NCR. Simultaneously, step up longer term systemic action to eliminate dirty industrial fuels, up-scale public transport, and minimise waste burning and dust generation for sustained air quality impact.”

In a post-Diwali air quality data, CSE has analysed that how Diwali night has ushered in the season’s first severe pollution peak due to the bursting of firecrackers in Delhi and the towns in the National Capital Region (NCR) including Gurugram, Faridabad, Noida and Ghaziabad.

The bursting of firecrackers has undone the comparatively cleaner trend achieved so far in the September 15 to October 27 period.

“Ghaziabad has become the first among its peers in the region to experienced season’s first 24-hour average severe pollution on the day of Diwali. The air in the other cities and towns is also expected to follow suit post Diwali,” said CSE in the statement.

CSE has analysed the Central Pollution Control Board’s (CPCB) real-time data on PM 2.5 concentrations to assess three things — the trend during Diwali, the weekly trend before Diwali, and the overall trend since September 15.

It has also compared the levels between the 2019 and 2018 Diwali days. It may be noted that in 2018, Diwali had occurred on November 7 — 10 days later than this year in the season, and it was colder. This analysis has also taken into account the trends in wind speed.

In the data, CSE showed that this year Peak Diwali pollution is somewhat similar to the previous year Diwali, but dissipates faster.

From a very clean afternoon, the change to severe pollution levels after 10 pm at night was drastic. There was a 10-fold jump in PM 2.5 concentrations between 5 pm and 1 am due to bursting of firecrackers. The peak level during 1 am to 3 am was quite similar to the peak levels observed in 2018 during Diwali. This was a warmer and windier Diwali than in 2018. However, during 2018, the peak pollution continued until 8 am, whereas this year, the peak showed a sharper fall after 3 am,” according to CSE.

This year weekly trends in PM 2.5 level, the air was much cleaner before Diwali compared to that in the previous year, this shows the overwhelming role of firecrackers in building the severe peak on Diwali night.

“It may be noted that this year, there were no severe pollution days during the week preceding Diwali. In the previous year, the region had already experienced a couple of days of severe pollution, with many more days in the ‘very poor’ category.”

“This year, only Ghaziabad has experienced the season’s first 24-hour average severe pollution on Diwali day. However, there is an early indication that air quality in the post-Diwali days could deteriorate to ‘severe’ category,” CSE analysed.

Moreover, the onset of ‘poor’ and ‘very poor’ days has been delayed this winter. These have started to occur only after October 10. But during 2018, there were more such days, largely starting as early as September 26. Nearly all cities and towns had experienced severe pollution days even before Diwali (October 30, almost a week before Diwali).

It is important to note that overall pollution levels are comparatively lower in Delhi and NCR towns since September 15. While favourable weather conditions have contributed to this trend, the role of ongoing action and emergency interventions have also been important. This has prevented build-up of pollution to ‘very poor’ and ‘severe’ levels before Diwali and has also enabled quicker dissipation of pollution post-Diwali (as observed so far – until 4 pm today).

It is more important to note that during 2019, there have been days with wind speeds lower than in 2018, and yet pollution has not exceeded 2018 levels. Even on days with better wind conditions in 2018 leading to Diwali, the pollution level was higher compared to this year. It shows that the overall pollution load in the city in 2018 must have been higher.