In 1985, M.C. Mehta, a lawyer and head of his own environmental NGO, filed a public interest litigation (PIL) in the Supreme Court of India to enforce the 1981 Air (Prevention and Control of Pollution) Act in the environs of India's National Capital Region (NCR). In 1988, World Bank experts had advised the Indian government that given the extent to which air pollution in the National Capital Region came from an increasingly large fleet of passenger vehicles, an effective policy would be to mandate relatively clean compressed natural gas (CNG) in public transportation vehicles. Although the government had actively considered a series of policies, it had failed to implement any. By the early 1990s, New Delhi was the fourth-most polluted city in the world. By June 1998, the sub-particulate matter concentration in Delhi's air was three times higher than the standards set by India's Central Pollution Control Board.
