Residents of Leeds and Sheffield are at risk from dangerously high levels of air pollution, the World Health Organisation has said.
The cities were among nine urban areas in the UK named in a report by the global health body as failing to meet guidelines on air quality.
WHO said most cities that measured outdoor air pollution were putting residents at risk of respiratory disease and other health problems by failing to meet the recommended levels.
“Too many urban centres today are so enveloped in dirty air that their skylines are invisible,” said Dr Flavia Bustreo, WHO’s assistant director-general for family, children and women’s health.
“Not surprisingly, this air is dangerous to breathe.”
WHO’s air quality database monitors 1,600 regions around the world, including 36 in Britain.
Earlier this year the organisation estimated that outdoor air pollution was responsible for the deaths of 3.7 million people globally during 2012, from heart disease and stroke, respiratory illnesses and cancers.
Last month a report from Public Health England (PHE) said long-term exposure to air pollution contributed to 2,567 deaths in Yorkshire and Humberside in 2010.
The worst area was Hull, at 5.9 per cent, closely followed by Rotherham and Wakefield at 5.7 per cent and Doncaster at 5.6 per cent. In Leeds and Sheffield the figure was 5.5 per cent.
Of those, only Leeds and Sheffield were named in the WHO report, along with Chesterfield, Birmingham, London, Nottingham, Sheffield, Southampton, Stoke-on-Trent and Thurrock.
Others cities, including Manchester, Bournemouth and Northampton could not provide comparable statistics on air quality.
Dr Carlos Dora, coordinator for interventions for healthy environments at WHO, said: “We cannot buy clean air in a bottle, but cities can adopt measures that will clean the air and save the lives of their people.”
PHE said that air quality had improved “considerably” in the UK in recent decades due to new, cleaner technology and tighter environmental legislation.
But it said that local action can be taken to reduce the emissions of these man-made particles and people’s exposure to air pollution.
Labour’s shadow environment minister Barry Gardiner said: “29,000 people in the UK are dying every year because of air pollution in our towns and cities and yet the Government has no strategy.
“This World Health Organisation report shows that there is an urgent need for the Government to take action against this silent killer and reduce the level of air pollution.
“This report shows that the Government’s failure is increasing the health inequalities that blight our cities, including Nottingham, London and Birmingham.”
Friends of the Earth campaigner Jenny Bates said: “Air pollution is bringing death and misery to millions of people across the world. Tackling it should be an urgent priority for governments and local authorities.
“Tens of thousands of people die prematurely in the UK every year because of poor air quality, and health limits are regularly breached - especially in London.
“Tough measures are needed to tackle the causes of our dirty air, particularly traffic pollution. They should include cleaner vehicles, encouraging people to drive less through better public transport and cycling facilities, and ending plans to build more roads.”