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

Initiatives to reduce vehicular air pollution in Delhi

• Mandatory CNG for public transport: on Supreme Court orders in the late 1990s, Delhi converted its entire fleet of public transport vehicles — buses, taxis and auto-rickshaws — to run on Compressed Natural Gas (CNG) instead of diesel or petrol. CNG burns more cleanly, producing far less particulate matter, carbon monoxide and unburnt hydrocarbons than diesel.
• Phasing out old vehicles: old, highly polluting commercial vehicles were phased out and replaced with CNG-compliant ones.
• Lead-free petrol and low-sulphur diesel: the use of lead-free petrol was made mandatory, and the sulphur content in diesel was progressively reduced, since sulphur compounds contribute to air pollution and reduce the efficiency of catalytic converters.
• Mandatory catalytic converters: vehicles were required to be fitted with catalytic converters to reduce carbon monoxide and nitrogen oxide emissions.
• Stricter emission norms: progressively tighter Bharat Stage emission standards were enforced for all new vehicles.

Has air quality improved? …

Answer in two clearly separated parts: first list the specific initiatives (CNG mandate for public transport, lead-free petrol, low-sulphur diesel, catalytic converters, emission norms), then directly answer the "has air quality improved" …

• Naming only "CNG" in general without specifying it was mandated for the public transport fleet under a Supreme Court directive.
• Answering only the first half of the question (the initiatives) and skipping the second half (whether air quality actually improved). …