Greenpeace India in its report 'Out of Sight - How coal burning advances India's Air Pollution Crisis' released on Monday, claimed thermal power generation is causing a "steady" deterioration in the overall air quality in North India.

"The report reveals coal as the largest overlooked source of air pollution and identifies air pollution emission hotspots in India visibly linked to thermal power plants in the area. Satellite based analysis from 2009 to 2015 reveals the thermal power plant clusters in Singrauli, KorbaRaigarh, Angul, Chandrapur, Mundra and NCR were the source of SO2 (sulphur dioxide) and NO2 (nitrogen dioxide) emission growth in India over the past five years, showing nationwide increase of 13 per cent and 31 per cent respectively for PM2.5 and SO2," the NGO said in a statement.

It said using similar data, earlier studies have shown an increase of 20 per cent in the regional trends for NO2 levels over the last decade. Secondary particulate matter formed by SO2 and NO2 is one of the major contributors to PM2.5 levels.

The NGO said that multiple research studies have emphasised 30 per cent to 34 per cent of total PM2.5 concentration in India is contributed by the secondary particulates, most of which come from burning of fossil fuels. Large industrial clusters, hotspots of SO2 and NO2 emissions, are found to be highest coal guzzlers, it said.

"To address the air pollution crisis, we need to accept that coal burning is responsible for increased emissions of SO2 and NO2 contributing to overall particulate matter concentration and identify the correlation between such increases and major coal consuming hot-spots in the country. An estimated 75-90 per cent of sulphates and 50 per cent nitrates are formed from SO2 and NOx emissions primarily originating from the thermal power plants. The satellite images clearly show that the emissions are highest in the regions where a lot of coal is being burnt," said Sunil Dahiya, a Greenpeace India Campaigner.

Particulate matter, or PM, is the term for particles found in the air, including dust, dirt, soot, smoke, and liquid droplets. Particles less than 2.5 micrometres in diameter (PM2.5) are referred to as "fine" particles and are believed to pose the greatest health risks. Because of their small size (approximately 1/30th the average width of a human hair), they can lodge deeply into the lungs.

Greenpeace India said the current installed capacity of thermal power generation is causing a "steady deterioration" in the overall air quality in North India.

A recent report by IIT Kanpur on Delhi's air pollution indicated that it would need a comprehensive and systematic plan in place for an area of at least 300 kilometres around Delhi to make a meaningful impact on the air quality. The report said that urgent, coordinated inter-agency efforts is needed to resolve the crisis not just for Delhi but to address the pollution in most north Indian cities.

"Greenpeace is calling for an ambitious and systematic national clean air action plan with focused targets, clear timelines and demonstrable accountability towards public health. Now that we have a clear understanding of the primary and secondary sources causing pollution, it provides us an opportunity to test India's emergency response plan on air pollution," added Dahiya.