NEW DELHI – India’s capital has recorded the world’s most toxic air as seasonal fires to clear farmland added to pollution from vehicles, construction and coal-fired power plants.

New Delhi’s air quality index climbed to as high as 346 early on Monday, the most among 110 cities around the world tracked by Swiss company IQAir. The same reading in Mumbai rose to as high as 177.

The current poor air quality is due to a drop in temperatures and slow wind speeds, said Dr Anju Goel, an air quality research fellow at The Energy and Resources Institute, a Delhi based think-tank. That has hampered the dispersal of pollution, she said.

The Indian capital also recorded a concentration of fine particulate matter, or PM2.5, of 296 micrograms per cubic m of air, almost 20 times the World Health Organisation’s recommended level of 15, according to IQAir. Fine particulate air pollution shortens the average life expectancy of Indians by 5.3 years, a University of Chicago study shows.

India’s central and state governments have introduced a raft of policies to try to tackle air pollution, but their efforts have so far proved ineffective.

While agricultural fires in areas around Delhi have fallen significantly over the past five years, other sources of pollution, including those from construction and inefficient cooking stoves, are getting worse because of population growth, according to Mr Sunil Dahiya, an analyst at the Centre for Research on Energy and Clean Air.

Power plants operating around the capital were supposed to have installed pollution controls, but poor enforcement means that most have not yet done so, he said.

The situation is likely to get worse unless there is better regulation and compliance, Mr Dahiya said. BLOOMBERG