The eastern metropolis needs to reduce its annual average pollution levels by 44 per cent to be able to meet the clean air standards, with a special focus on vehicular emissions, an analysis said on Friday.

"The national annual ambient air quality standard is 60 microgram per cubic metre," the Centre for Sciencs and Environment said in a rapid diagnostic analysis that looked into whether key metro cities figure in terms of pollution and carbon footprint of motorisation.

It pointed out that of all the major metro cities in India, Kolkata's transport sector had the smallest pollution and carbon footprint.

However, the analysis warned the city was at "serious risk of losing this advantage" as it was encouraging car-centric planning and infrastructure.

"Kolkata has the highest share (among all metros) of public transport and walking -- 89 per cent of the population uses these modes. It also has the most diverse system of public transport among all metro cities -- bus, metro, tram, suburban rail and waterways. Its policymakers and planners should recognise and leverage this advantage," it said.

In terms of carbon footprint, a car user has 6.5 times more carbon footprint than a two-wheeler rider and 10.6 times more than a bus user, in the city.

"With growing motorisation, this will get worse -- in 2010-12, vehicle registration was in the range of 8-11 per cent; after 2012, this has shot up to 158 per cent," the analysis said.