Smoke and sulphur: on sulphur dioxide emissions, public health

The axe has dropped. The Environment Ministry has exempted the majority of India’s coal-fired plants from mandatorily installing Flue Gas Desulphurisation (FGD) systems, which are designed to cut sulphur dioxide (SO₂) emissions. In effect, this undermines its own mandate from 2015 that required all such plants — there are about 180 of them now, comprising 600 units — to install these systems. While these were expected to be in place by 2017, only about 8% of the units have actually installed FGD — nearly all by the public-sector National Thermal Power Corporation (NTPC). SO₂ is among the gases monitored by the Central Pollution Control Board (CPCB) as exposure beyond a degree can be harmful. Less appreciated is its propensity to form sulphates in the air and contributing to particulate matter pollution. In general, India’s average ground-level SO₂ measurements have been below the permissible levels — one among several reasons that there has not been a sense of urgency in implementing FGD norms. The official reasons are the limited number of vendors in India, high installation costs, the potential rise in electricity bills, and disruptions due to the COVID-19 pandemic. While the latest deadlines flew by in 2024, the Environment’s Ministry’s decision — it follows consultations with scientific institutions and new commissioned studies — is a sharp disavowal of the current policy. An expert appraisal committee says that Indian coal is low in sulphur; SO₂ levels in cities near plants with operational FGD units do not differ significantly from those without these units, and all of these were anyway well below permissible levels. The committee had said that concerns about sulphates are unfounded. It also argued, echoed by the Minister for Power, that sulphates had a beneficial side-effect in suppressing warming from greenhouse gas emissions. Thus, reducing sulphates would actually worsen warming and compromise India’s climate goals. While IPCC assessments do account for the heat-suppressing action of sulphates, nowhere is it projected as an unalloyed good.

A minority of plants, about a fifth — those within a 10 km radius of the NCR; in cities with a population of over a million, or known to be in pollution hotspots — must install FGDs by 2028. This seems to suggest that what determines their installation is the location of a coal plant and not whether FGDs are effective or SO₂ is harmful. This is a rare instance when there are different environmental standards within India on controlling exposure to a pollutant. While it is not unscientific to revise understanding of the harms or benefits of substances, this needs debate in the public domain before a policy is changed. Otherwise it amounts to undermining India’s commitment to scientifically informed public health.