Air pollution in the National Capital has been causing distress among the Delhiites for quite sometime. While the blame game continues between the state’s current and ex governments, a Finalnd-headquartered think-tank – Centre for Research on Energy and Clean Air (CREA), has conducted an analysis on what’s causing the AQI to drop to new lows this year.
The analysis found that nearly one out of every three units of Delhi’s yearly PM2.5 air pollution comes from secondary ammonium sulfate. This pollutant is formed through chemical reactions linked to emissions from factories, coal-based power plants, and farming activities, which then becomes a major part of the air during the city’s most polluted days.
The substance behind the air abuse
Ammonium sulfate is a pollutant that forms in the air when sulphur dioxide from sources such as coal power plants and industries changes into sulfate and then combines with ammonia released mainly from farming and other activities. This process becomes stronger in humid weather, adding to high PM2.5 pollution in Delhi and the wider National Capital Region.
The issue is more worrying because India releases more sulphur dioxide than any other country in the world. At about 11.2 million tonnes, its SO2 emissions are second only to China, an earlier analysis by CREA had pointed out.
The latest study showed that ammonium sulfate makes up nearly half of Delhi’s PM2.5 pollution after the monsoon and about 41% during winter. In comparison, its share drops to around 21% in the summer and monsoon months.
This suggests that Delhi’s worst air pollution spells are mainly caused by sulphur dioxide released across the region and by chemical reactions in the air, not just by pollution coming directly from local sources.
Nearly half of India’s PM2.5 pollution forms in the air itself, analysis finds
Secondary particles play a major role in India’s PM2.5 pollution. A large share of these tiny particles is not released directly but forms in the air through chemical reactions involving gases like sulphur dioxide and ammonia. An analysis by CREA found that such chemically formed pollution can make up as much as 42% of the country’s PM2.5 load.
At the national level, states with a heavy presence of coal-based power plants showed the highest levels of ammonium sulfate in PM2.5 pollution. Chhattisgarh topped the list with a 42% share, followed closely by Odisha at 41%. Jharkhand and Telangana each recorded around 40%.
Other states also showed high levels of this secondary pollution. Bihar had a share of about 39%, while Maharashtra, Andhra Pradesh and West Bengal were close behind at 38% each. Uttar Pradesh and Madhya Pradesh followed with around 37%.
The analysis pointed out that nearly four out of five coal-fired power plants have been allowed to skip installing pollution-control systems that remove sulphur dioxide. This has weakened control at the source. The study stressed that bringing back the 2015 emission rules is important to make such systems mandatory, which would help cut the formation of ammonium sulfate and reduce PM2.5 levels.
One of the study’s authors, Dr Manoj Kumar, said the findings are important as the National Clean Air Programme is being reviewed, reported The Indian Express. He noted that the programme mainly focuses on PM10, even though a large part of PM2.5 pollution is created in the air from gases released by various sources.