New Delhi: Residents breathe "unacceptable levels" of toxic air in Delhi as the national capital city is gasping because of skyrocketing levels of air pollution, according to a new data.

However, underground Metro rail protects from the high level of pollution, says data prepared by the Centre for Science and Environment (CSE).

Shunned as one of the world's most polluted cities, Delhi is literally gasping for breath, with air pollution levels seeming to be skyrocketing without any restraint, it says.

According to it, exposure in all transport modes in Delhi is very high with the average levels recording at 2 to 4 times higher than the background levels reported by the state pollution control board.

The traffic police is breathing "unacceptably high levels of toxic air", it says. Monitoring carried out at the ITO crossing showed peak exposure at eight times the ambient level.

"Open modes like autorickshaws, walking and cycling have the highest exposure. During off-peak hours, all modes show lower levels: Difference between peak and off-peak was as follows -- autos 1.3 times higher; walking 1.5 times higher, and buses 2.5 times higher," the CSE says.

It says underground Metro with sealed environment shows lower levels of about 209 microgramme per cubic metre. The overhead metro had levels of 330 microgramme per cubic metre.

Pollution levels peak near junctions and in traffic jams: "In a traffic jam on a stretch close to Paharganj, levels peaked at 1,170 microgramme per cubic metre. At a traffic jam near Govindpuri Metro Station, the peak level was 725 microgramme per cubic metre," the data says.

Noting that proximity to diesel trucks lead to extremely high exposure, the CSE data says a cycle rickshaw ride on NH-24 in close proximity to truck traffic recorded a range of 651 to 2,000 microgramme per cubic metre.

Even cars do not help. It says monitoring inside the car was carried out during off-peak hours and the average levels were found to be double the ambient levels.