Air pollution is responsible for nearly one in four of childhood asthma cases in a city synonymous with the Industrial Revolution, a study suggests.

Scientists used computer simulations to assess the impact of exposure to irritant gases called nitrogen oxides in Bradford, finding that up to 38 per cent of all annual cases of childhood asthma in the may be attributable to air pollution.

Pollution from road vehicles alone was linked to 24 per cent of cases, compared to an international average of six to 14 per cent.

Overall, rates of childhood asthma cases in Bradford are higher than the national average of around one in 11, with some studies suggesting more than twice the rate, as are emergency hospital admissions for asthmatic children under 16 years of age.

"Traffic-related air pollution is a real concern to the community,” said Dr Haneen Khreis, who led the research at the University of Leeds.

"Our team's previous research has shown that children exposed to high levels of traffic-related air pollution have a higher risk of developing asthma.

"Quantifying the number of childhood asthma cases that are directly attributable to traffic-related air pollution has not been done in the past and as we show now, a significant portion of cases is largely preventable."