NEW DELHI: India’s national capital region (Delhi-NCR) is back in the news for its hazardous levels of air pollution. It has been the top polluted city in the world for the past many days. With more than half of the households in Delhi-NCR having at least one person suffering from lung illness, the capital is in the midst of a health emergency.
Most people blame the paddy stubble burning in Punjab and Haryana, and solid waste burning in Delhi-NCR for the situation. However, a major constituent of the fine particulate matter, PM2.5, has secondary aerosols such as sulphur (SOx), nitrate (NOx) and ammonia (NHx), whose main source is coal-fired thermal power plants (CFTPPs) in Delhi-NCR. A new analysis by the Centre for Research on Energy and Clean Air (CREA) shows that thermal power plants (TPPs) in NCR emit 281 kilotonnes of SO2 annually—16 times more than the 17.8 kilotonnes emitted by burning 8.9 million tonnes of paddy straw. Crop residue burning causes a seasonal spike in Delhi-NCR pollution whereas the TPPs cause persistent year-round pollution. Yet, lopsided action is taken against farmers while TPPs get free-wheeling leniency.
Why control SO2 concentration
SO2 is a significant air pollutant with direct and indirect effects on human health, the environment and climate. It is a precursor to the formation of the fine particulate matter (PM2.5), which has been linked to severe health issues, including respiratory and cardiovascular diseases. Exposure to high levels of SO2 can cause irritation in the eyes, throat and lungs, aggravating conditions such as asthma and bronchitis. Long-term exposure is associated with an increased risk of heart attack, stroke, and premature death. Moreover, SO2 contributes to the formation of acid rain, which can damage ecosystems and harm aquatic life. In 2023, India became the top emitter of SO2. According to an analysis by the CREA, India emitted 6,807 kilotonnes, followed by Turkey (2,206 kilotonnes), Indonesia (2,017 kilotonnes), South Africa (1,705 kilotonnes) and others.
Regulatory control
On December 7, 2015, the Union Ministry of Environment, Forest and Climate Change issued a notification to cut air pollution by reducing the concentration of SOx, NOx and mercury emissions from TPPs. It made it mandatory for thermal power plants to install flue gas desulfurization (FGD) units to curtail the emission of SO2 from the stacks so as to comply with its emission limits. However, the industry missed several deadlines to install FGD plants. As of now, less than 8% of CFTPP capacity has completed FGD installation to control SO2 emissions.
FGD technology
The Indian Institute of Technology, Delhi (IITD) conducted a study on the surface concentration of two major air pollutants, SO2 and sulphate aerosols, in the surrounding region of TPPs through different modelling with the help of satellite data.
It found that the implementation of FGD technology in TPPs can result in reducing concentration of SO2 by up to 55% as far as 60-80 km away from the location of the TPPs. It also showed a significant decrease in the concentration of sulphate (SO4) aerosols up to 30% as far as 200 km from the TPP site.
The study found that the maximum contribution to SO2 surface mass concentration over Delhi-NCR in December came from the energy sector emissions (~63%), sulfate (SO4) aerosol from the transportation sector emissions (~33%) followed by the energy sector (26%).
The U-turn
However, NITI Aayog, the government’s think tank, recently recommended stopping of new orders for installation of FGD units. In its office memorandum dated September 24, 2024, it cited a draft study report on “Analysis of Historical Ambient Air Quality Data Across India for Developing a Decision Support System by National Environmental Engineering Research Institute (CSIR-NEERI), Nagpur” to recommend no further installation of FGDs.
The researchers measured the concentration of SO2 at 467 Continuous Ambient Air Quality Monitoring Systems operated by the Central Pollution Control Board and 486 TPPs across India for four years. They determined that very few sites (only 13) have the highest SO2 level beyond the prescribed limit of 80 µg/m3, that too only in the fourth quartile range (less than 25% of the data).
The CSIR-NEERI data does not suggest that SO2 emission from coal-based power plants is responsible for adversely impacting the ambient air quality standards. It states that at present, in most of the observations, the ambient air quality standards for SO2 are being met.
It recommends a pause in the installation of additional equipment like FGD, and analysis of their contribution to the total cost of power generation. It also suggests that the government focus on controlling the release of harmful particulate matter instead of mere SO2 policing.