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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.

How bad is air pollution in Delhi?

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

  • Delhi air turns toxic after Diwali fireworks

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.

What are PM 2.5 particles?

  • Particulate matter, or PM2.5 is a type of pollution involving fine particles fewer than 2.5 microns (0.0025mm) in diameter
  • A second type, PM10, is of coarser particles with a diameter of up to 10 microns
  • Some occur naturally – e.g. from dust storms and forest fires, others from human industrial processes
  • They often consist of fragments that are small enough to reach the lungs or, in the smallest cases, to cross into the bloodstream as well

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:

  • crop burning by farmers in Punjab and Haryana states
  • exhaust emissions from vehicles
  • construction and industrial activity in Delhi and surrounding areas
  • weather patterns across the region trapping pollutants in the atmosphere

Image source, AFPImage caption, Smog is a regular issue around this time of the year in DelhiHow does Diwali affect the air quality?

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.

Image source, Getty ImagesImage caption, The sale and use of firecrackers is banned in many states

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.

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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.

What are the other factors?

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

Image source, Getty ImagesImage caption, A huge layer of smoke covers Delhi and north India post Diwali

The other caveat is around vehicle traffic, which increases in the Diwali period when people go out to buy gifts and visit family and friends.

Could the higher concentrations of PM2.5 be because of more traffic on the roads rather than fireworks?

The authors say they want to address this in future research.

Fireworks do contain other toxic substances, including heavy metals.

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

  • PM10 particles
  • sulphur dioxide
  • nitrogen dioxide
  • ozone
  • iron
  • lead
  • manganese
  • copper
  • beryllium
  • nickel

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 are also produced by vehicle emissions.

However, there probably is some logic to attempts to restrict the use of fireworks – in that they contribute to an existing problem in cities that are already some of the most polluted on earth.

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

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