Diesel fumes cause lung cancer, the World Health Organisation declared Tuesday, and experts said they were more carcinogenic than secondhand cigarette smoke.

The WHO decision, the first to elevate diesel to the “known carcinogen” level, may eventually affect some American workers who are heavily exposed to exhaust. It is particularly relevant to poor countries, where trucks, generators, and farm and factory machinery routinely belch clouds of sooty smoke and fill the air with sulfurous particulates.