There are 8 x 10^6 cars in New Delhi. It is the most polluted city in the world.
The air has 16x the safe concentration for PM2 (a pollutant). New Delhi has 300-400 mgcm^-3; a safe concentration would be 25.
Suggestions to improve this include alternating days for driving, or limiting the number of big deisel vehicles. 700,000 more people are in public transport, but pollution can still be 20x the safe levels.