The central government has once again extended the deadline for coal-based thermal power plants to comply with sulphur dioxide emission norms and has fully exempted those located away from critically polluted areas or cities with a population of over 1 million.In a notification dated July 11, the environment ministry said the compliance deadline for Category A plants, located within a 10-km radius of the National Capital Region or cities with a population of over 1 million, has been extended from December 2024 to December 2027.Category B plants, situated within a 10-km radius of critically polluted areas or non-attainment cities, will now be assessed on a case-by-case basis instead of adhering to the earlier 2025 deadline.Category C plants — all others not falling under Category A or B — have been completely exempted from the sulphur dioxide norms, provided they meet the prescribed stack height criteria. These plants were earlier required to comply by December 2026.Flue gas desulphurization units are installed in coal-fired power plants to control sulphur dioxide emissions, a major air pollutant. SO2 converts into fine particulate matter, which can penetrate deep into the lungs and cause a range of diseases, leading to millions of deaths each year.The ministry said it had received numerous representations seeking exemption or relaxation in the timelines of the emission standards due to factors, such as the "limited availability of technology providers, its techno-economic feasibility, negative impact of the Covid pandemic on supply chain, price escalation due to high demand and low supplies, low Sulphur dioxide concentration in ambient air and heavy burden on consumer due to increase in electricity prices etc".It added that it had also received an "explicit recommendation" from the Ministry of Power in this regard.According to the notification, several studies were conducted by research institutions regarding the effectiveness and rationale behind the SO2 standards and their role in the overall ambient air pollution of the region.The ministry said consultations were held with the industry, the Ministry of Power, the Central Pollution Control Board, scientific institutions and other stakeholders regarding the emission standards and their timeline.It added that a committee was constituted in the CPCB to "examine the issue in totality, assess the available study reports, other relevant materials and other related factors and make a recommendation on applicability of these standards and its timeline".The CPCB, after detailed analysis, submitted its recommendation based on its study on the National Ambient Air Quality Standards of SO2 across most regions of the country; resource conservation in terms of avoiding additional consumption of water, auxiliary power and limestone; and the increase in carbon footprint or carbon dioxide emissions due to operation of the deployed control measures and mining and transportation of limestone required for these measures.It also considered the techno-economic feasibility of implementing such control measures in all coal or lignite-based thermal power plants and the application of the precautionary principle for control and abatement of air pollution in densely populated and other air pollution-sensitive areas, the ministry said.