NEW DELHI: The mandatory retrofitting of coal-fired generation plants with mechanisms to reduce sulphur emission will apply to only units within 10 km of cities with population exceeding 10 lakh instead of all power stations under a 2015 mandate.The revised policy, notified on Saturday, is expected to reduce the cost of power by 25-30 paise per unit, officials and experts involved in the revision of the earlier mandate for installation of FGD (flue gas desulphurisation) units at all power plants said.The new norm lets off the hook 79% of the country’s thermal generation capacity, a fact that environmental activists have used to criticise the revision. But officials argued that the “evidence-based recalibration” makes the policy “focused, efficient and climate-conscious.”For example, they said, under the revised policy, new plants in critically polluted areas or non-attainment cities will be evaluated on a case-by-case basis instead of an omnibus application that would push up the cost of power.The notification justified the revision, saying it is in line with the analysis by the Central Pollution Control Board, which found increased carbon dioxide emissions resulting from the operation of existing control measures. Additionally, studies by IIT-Delhi, CSIR-NEERI and the National Institute of Advanced Studies put ambient sulphur dioxide levels in most parts of the country within the National Ambient Air Quality Standards.Power producers have been opposing the blanket FGD mandate for all plants due to the high cost involved. Industry estimates put the cost of installing FGDs at all power plants at Rs 2.5 lakh crore, or Rs 1.2 crore per megawatt. This, industry representatives had said, would jack up tariff for consumers. Additionally, the average timeline of 45 days for each unit was also cited as a threat to grid stability during peak seasons.Differentiated compliance based on proximity to urban populations and the sulphur content of the coal used will ease the burden on power producers, industry executives said. Indian coal typically has a sulphur content of less than 0.5% and due to high stack heights and favourable meteorological conditions, dispersion of SO2 is efficient.Measurements across multiple cities showed sulphur oxide levels ranging between 3 and 20 micrograms per cubic meter, significantly below the NAAQS threshold of 80 micrograms per cubic meter. The officials said studies had also questioned the environmental and economic efficacy of a universal FGD mandate in the Indian context.