in Delhi during winters has declined notably since 1998 due to rising air pollution. India's Ministry of Earth Sciences published a research paper in October 2018 attributing almost 41% of PM2.5 air pollution in Delhi to vehicular emissions, 21.5% to dust/fire and 18% to industries. The director of Centre for Science and Environment (CSE) alleged that the Society of Indian Automobile Manufacturers (SIAM) is lobbying "against the report" because it is "inconvenient" to the automobile industry. Environmentalists have also criticised the Delhi government for not doing enough to curb air pollution and to inform people about air quality issues. In 2014, an environmental panel appealed to India's Supreme Court to impose a 30% cess on diesel cars, but till date no action has been taken to penalise the automobile industry. Most of Delhi's residents are unaware of alarming levels of air pollution in the city and the health risks associated with it. In 2020, annual average PM2.5 in the Delhi, stood at 107.6 µg/m³, which is almost 21.5 times the World Health Organization PM2.5 Guideline (5 µg/m³: set in September, 2021). These pollution levels are estimated to reduce the Life Expectancy of an average person living in Delhi by almost 10.1 years. However, , awareness, particularly among the foreign diplomatic community and high-income Indians, was noticeably increasing. Since the mid-1990s, Delhi has undertaken some measures to curb air pollution—Delhi has the third-highest quantity of trees among Indian cities and the Delhi Transport Corporation operates the world's largest fleet of environmentally friendly compressed natural gas (CNG) buses. In 1996, the CSE started a public interest litigation in the Supreme Court of India that ordered the conversion of Delhi's fleet of buses and taxis to run on CNG and banned the use of leaded petrol in 1998. In 2003, Delhi won the United States Department of Energy's first 'Clean Cities International Partner of the Year' award for its "bold efforts to curb air pollution and support alternative fuel initiatives". The Delhi Metro has also been credited for significantly reducing air pollutants in the city. However, according to several authors, most of these gains have been lost, especially due to stubble burning, a rise in the market share of diesel cars and a considerable decline in bus ridership. According to CSE and System of Air Quality Weather Forecasting and Research (SAFAR), burning of agricultural waste in nearby Punjab, Haryana and Uttar Pradesh regions