Levels of benzene, a cancer-causing VOC, were astounding, Prevot's team found.
Scooter exhaust during idling had as much as 300,000 micro grams (mcg) of benzene per cubic metre, or 146 parts per million (ppm), the scientists found.
By comparison, the European Union (EU) sets a safety level for annual exposure of five mcg/cu. m., while health watchdogs in the United States recommend that workers wear special breathing equipment when exposed to benzene levels exceeding 1ppm for 15 minutes.
"The (benzene) emissions are huge. Thinking about being on a bike and breathing the emissions from an idling scooter in front at a traffic light is rather disturbing," Prevot said in an email interview.
The paper calculated that in cities such as Bangkok, two-stroke scooters could contribute between 60 and 90 per cent of all roadside primary particulate matter, carbon particles that result directly from fossil-fuel combustions, even though they account for only 10 percent of fuel consumption.
The scooters' overall impact may even be a conservative estimate, Prevot said.
Auto rickshaws tested in India yielded five times more emissions on average than the European scooter, he said.
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