Downplaying sulphates, ignoring transboundary pollution — A flawed shift in India's FGD strategy
A high-level meeting was recently held under the leadership of the Principal Scientific Adviser to the Government of India to discuss the way forward on the installation of Flue Gas Desulfurisation (FGD) systems in thermal power plants.
The meeting brought together senior officials from the Ministry of Power, the Ministry of Environment, Forest and Climate Change, the Central Electricity Authority (CEA), the Central Pollution Control Board (CPCB), NITI Aayog, as well as researchers from IIT Delhi, CSIR-NEERI, and NIAS Bangalore.
During the meeting, the Principal Chief Engineer-II of the CEA delivered a detailed presentation outlining the findings and recommendations from various studies conducted by IIT Delhi, NEERI Nagpur, and NIAS Bangalore. These studies evaluated the impact of emissions — particularly sulphur dioxide (SO₂)—from thermal power plants on ambient air quality.
Key findings and recommendations
The IIT Delhi study, conducted in 2024 with support from the Ministry of Power, examined ambient SO₂ concentrations in ten cities, covering a range of geographic and developmental categories.
The study reported daily mean SO₂ concentrations ranging from 2.97 to 16.17 micrograms per cubic metre — well below the National Ambient Air Quality Standard (NAAQS) limit of 80 micrograms per cubic metre. Importantly, it found no significant difference in SO₂ levels between cities with thermal power plants equipped with operational FGDs and those without them.
The NEERI Nagpur study, supported by NITI Aayog, analysed 5,792 samples of particulate matter collected from various regions across India.
The findings indicated a low elemental sulphur content in the samples, with a maximum concentration of 8 micrograms per cubic metre after outlier values were excluded. This suggested that SO₂ emissions contribute minimally to overall ambient air pollution levels in the form of particulate matter.
The study by NIAS Bangalore revealed that over 92 per cent of electricity generated by Indian thermal power plants comes from coal with sulphur content below 0.5 per cent, a level considered low by international standards. Crucially, the study estimated that mandating FGD installation in all thermal power plants by 2030 could result in a significant rise in Auxiliary Power Consumption.
This, in turn, could lead to an additional 69 million tonnes of CO₂ emissions during the period 2025 to 2030, while only reducing SO₂ emissions by 17 million tonnes over the same timeframe.
The current mandate for FGD installation stems from a 2015 study conducted by Professors Mukesh Sharma and Dikshit from IIT Kanpur. Their research found that secondary sulphate particles accounted for 8 to 21 per cent of PM2.5 pollution in Delhi during the winter months.
Based on these findings, the Environmental Pollution (Prevention and Control) Authority (EPCA) for the National Capital Region (NCR) recommended setting stack emission standards for SO₂, which led to a nationwide directive for FGD implementation in thermal power plants. However, before implementing these standards, the CPCB had not conducted similar studies on sulphate contributions from SO₂ emissions in regions outside the NCR.
After thorough deliberation, the meeting reached a consensus to submit a set of recommendations to the relevant ministries, proposing a categorised approach to FGD implementation.
For Category A thermal power plants — those located within a 10-kilometre radius of the NCR or in cities with populations exceeding one million — it was recommended that the precautionary principle be applied, and FGD requirements be retained.
Category B plants, located within a 10-kilometre radius of critically polluted areas or non-attainment cities, may be granted exemptions on a case-by-case basis, following joint reviews by the Ministry of Power or CEA and the Ministry of Environment or CPCB.
It was further recommended that thermal power plant units in either Category A or B that have completed 20 years of operation as of 31 March 2025 could be exempted from FGD installation, given the limited time left for cost recovery. For Category C plants, which comprise all remaining units not falling under Categories A or B, a general exemption was proposed.
CSE perspective: Ignoring the bigger picture
The Centre for Science and Environment has raised strong concerns about the shift in India's FGD strategy.
It argues that the ongoing discussions around FGD installation have largely centred on ambient SO₂ levels while ignoring a more critical aspect — the significant role of SO₂ in the formation of secondary PM2.5, a pollutant closely linked to severe respiratory and cardiovascular diseases. The CSE highlights that the 2015 IIT Kanpur study had already identified secondary sulphate aerosols as major contributors to PM2.5 concentrations in Delhi. Yet, the present narrative appears to downplay this crucial connection, especially the impact of transboundary SO₂ emissions from surrounding operational thermal power plants.
Of the 11 thermal power plants located around the Delhi-NCR region, four fall under Category A, while the remaining seven are classified as Category C.
Notably, several of the Category C plants have already invested in FGD technology. The new recommendations, if adopted, could create regulatory inconsistencies and potentially stall the progress already made, disincentivising further adoption of cleaner technologies and reversing compliance momentum achieved over the past few years.