Delhi pollution: Are Diwali fireworks to blame?

Air pollution levels have shot up in the Indian capital, Delhi, during the current festive season of Diwali.

A lot of attention has focused on the impact of fireworks and this year India's Supreme Court has recently allowed the use of green or eco-friendly crackers.

But how far are fireworks responsible for poor air quality?

There are studies which show that levels of some hazardous pollutants rise significantly during the Diwali period, but there are also other factors that could account for poor air quality.

Air pollution has become an increasingly serious problem in Indian cities in recent years.

Around 57,000 people died prematurely in Delhi in 2020 as a result of exposure to air pollution according to Greenpeace, despite the Covid lockdown.

Twenty of the world's 30 most polluted cities are in India according to a World Air Quality report for 2020, with the highest annual concentrations of PM2.5 - one of the most harmful particles for human health.

The levels are way above the recommended WHO guidelines for concentrations of PM2.5.

Around this time of year, Delhi and other cities in northern India, experience worsening air quality because of a combination of factors, not just because of Diwali fireworks.

These include:

Several states have banned the sale and use of fireworks during Diwali, but the implementation of the ban is weak in many states.

A 2018 study that has attempted to answer this question says there is a "small but statistically significant" effect from Diwali fireworks.

The study focused on five locations across Delhi, and looked at data gathered between 2013 and 2016.

Diwali is set according to the Hindu lunar calendar and usually happens in late October or early November.

The different dates are important because they enable the authors to take into account crop burning as a factor, because that starts at the same time of year.

"We used Nasa satellite data to establish when crop burning was happening in northern India," Dhananjay Ghei, one of the authors of the report told the BBC.

In two out of the four years, crop burning did not coincide directly with Diwali celebrations.

And they also point out that industrial activity in one location stopped because of the holiday, and factored the weather conditions into their calculations.

They found increases in concentrations of PM2.5 of almost 40% by the second day of the festival.

This then falls back to existing background levels soon after the end of Diwali.

And when looked at on an hourly basis, there was a rise of 100% for the five hours after 18:00 local time - the evening darkness period when most celebrations take place.

A report by Centre for Science and Environment, a non-profit based in Delhi, showed that the concentration of PM2.5 rose during Diwali in 2018, 2019 and 2020 in the capital.

Crop burning makes a significant contribution to poor air quality.

The government's monitoring system shows that this year, it accounted for 48% of PM2.5 particles in Delhi by 7 November, before going down a bit.

This was higher than the peaks recorded last year, and information from satellites that can detect active fires shows large parts of Punjab and Haryana states affected.

It should also be pointed out that not all fireworks produce a lot of PM2.5 particles, although the bigger ones tend to have larger concentrations.

But fireworks contain other toxic substances, including heavy metals.

A separate study done in the Indian city of Jamshedpur found significantly increased levels of the following substances during the Diwali period:

The government's own Central Pollution Control Board lists 15 substances in fireworks which it says are "hazardous and toxic".

Again, it needs to be added that some of these substances can also be produced by vehicle emissions.

Vehicle traffic does increase during Diwali when people go out to buy gifts and visit family and friends.

However, there's very little research that quantifies its exact contribution to poor air quality in this period.

This piece was first published in November 2018 and has been updated to reflect recent studies and pollution data.

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