As much as 14 percent of chronic childhood asthma may be caused by people living near busy roads and exposed to traffic pollution, a study in 10 European cities found Friday.

The study, released by the European Respiratory Journal, matched local health data with exposure to traffic pollution in Barcelona, Bilbao, Brussels, Granada, Ljubljana, Rome, Seville, Stockholm, Valencia and Vienna.

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They calculated proximity to busy roads, defined as carrying 10,000 vehicles per day.

“We estimated that an average of 33,200 asthma cases (14 percent of all asthmatic children) were attributable to near-road traffic-related pollutants,” the researchers wrote.

“In other words these cases would not have occurred if no one lived within the buffer zone or if those pollutants did not exist.”

The results were comparable, the authors said, to the burden associated with passive smoking — which the World Health Organisation blames for four to 18 percent of asthma cases in children.

Of the 10 cities studied, a third of the combined population was estimated to live within 75 metres of a busy road, and more than half within 150 metres.

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The team also measured traffic pollution’s impact on coronary heart disease among older adults, and estimated that 28 percent of such cases may be attributable to near-road exposure.

“Despite uncertainty and limitations, our results indicate that near-road traffic related pollution may be responsible for a large but preventable burden of chronic diseases and related acute morbidities in urban areas,” said the study authors.