Streets full of stationary vehicles with their engines running could be 10 times more polluted than busy roads full of slow-moving traffic, new research has revealed.
Such streets could also be warmer than surrounding urban areas by as much as five degrees Celsius, according to a study by the South China Morning Post. Environmentalists said the research could provide useful clues as to the effectiveness of a ban on idling engines, which takes effect in December.
Using a handheld device capable of measuring the carbon monoxide level every two seconds, readings were taken in seven streets in Causeway Bay and Mong Kok on the afternoon of August 13, while a very-hot-weather warning was in effect.
A section of Tung Choi Street in Mong Kok between Argyle Street and Fife Street - where dozens of minibuses were idling - had the highest carbon monoxide reading, at 23,223 micrograms per cubic metre of air.
While that was below the maximum level of carbon monoxide set in the government's air quality objectives, which is 30,000mcg, it was up to 12 times higher than the reading on a stretch of nearby Fife Street, where traffic was sporadic and there were no idling vehicles. It was also 30 times the level recorded by the Environmental Protection Department's Mong Kok air quality monitoring station, near Nathan Road in Prince Edward, at the time.
At a bus stop on Nathan Road, near Fife Street, the Post recorded a carbon monoxide concentration of 2,450mcg.
