New Delhi: India’s government plans to propose banning burning petroleum coke as a fuel nationwide to comply with a Supreme Court request as part of a long-running case to clean the country’s air, two government sources said on Friday.

The government proposal follows a ban ordered by the Supreme Court in October on burning petroleum coke in the region around the capital of New Delhi.

An oil refinery by-product, petroleum coke, or petcoke, is used as a fuel because of its higher energy content than coal, but it releases larger amounts of carbon dioxide and sulphur dioxide, which can cause lung disease and acid rain.

The government would expand the New Delhi ban across the country while still allowing petcoke to be used in the limestone and cement industries, said the sources who declined to be named. The proposal must be submitted to the court by June 30.

The sulphur emissions that are usually given off when petcoke is burnt are instead absorbed during the cement-making process. More than half of India’s petcoke demand of 27 million tonnes is imported, mostly from the United States, according to industry estimates.

India is home to the world’s 14 most polluted cities based on 2016 data measuring concentrations in the air of particulate matter smaller than 2.5 microns, which is particularly hazardous since they can lodge deep in the lungs. The country is also the world’s biggest consumer of petcoke.

The government decided to propose the nationwide restriction on petcoke after officials from the ministries of the environment, petroleum and natural gas, and commerce deliberated various options, including an outright ban on consumption and a ban only on imports, the sources said.

The ministries did not reply to emails seeking comment.

The government was ordered to submit the proposal so the Supreme Court can rule on a petition seeking steps to clear India’s air that was first raised in 1985.