What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?

Delhi has been categorized as the fourth most polluted city of the world in a list of 41 cities. Burning of fossil fuels has added to the pollution of air in Delhi.
Various steps have been taken to improve the quality of air in Delhi.
1. Introduction of CNG (Compressed Natural Gas): By the order of the supreme court of India, CNG-powered vehicles were introduced at the end of year 2006 to reduce the levels of pollution in Delhi. CNG is a clean fuel that produces very little unburnt particles.
2. Phasing out of old vehicles
3. Use of unleaded petrol
4. Use of low-sulphur petrol and diesel
5. Use of catalytic converters
6. Application of stringent pollution-level norms for vehicles
7. Implementation of Bharat stage I, which is equivalent to euro II norms in vehicles of major Indian cities.
The introduction of CNG-powered vehicles has improved Delhi’s air quality, which has led to a substantial fall in the level of CO₂ and SO₂. However, the problem of suspended particulate matter (SPM) and respiratory suspended particulate matter (RSPM) still persists.

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