Hong Kong diesel drivers beware. A volunteer army of vehicles spotters are on the prowl. According to The Wall Street Journal, these tailpipe smoke spotters are making a difference in Hong Kong’s air pollution.

The World Health Organization (WHO) finds that the air in Hong Kong is three times as polluted as New York’s and more than twice as bad as London’s. Nearby factories in southern China have been the scapegoat of Hong Kong’s pollution problem for a number of years, but environmental scientists say that vehicle pollution is to blame as well.

A 2007 study by Hong Kong University of Science and Technology found that local sources such as vehicles are the “primary influence” on the city’s air quality 53 percent of the time.

How are Hong Kong’s “smoky vehicle spotters” helping?

Before becoming a “SVS”, a person must go through rigorous government testing. This testing ensures that the spotter is fully capable of determining whether the amount of black smog exiting a vehicle’s tailpipe is, in fact, worthy of being reported or is within the legal limits.

Mr. Chan, a 41-year-old construction-industry executive, is one of Hong Kong’s 5,000-plus “smoky vehicle spotters”.

The WSJ says, “After Mr. Chan passed his spotter test, he found himself leaving the office for "spotting breaks." He got so good, he says, that he could recognize polluting vehicles from a mile away, nabbing up to 10 of them in a half-hour session. Today, he regularly devotes lunch breaks to staking out vehicles from a secret vantage point in the central business district.

‘I don't want to give away my location, or else drivers will know how to avoid me,’ says Mr. Chan, who got into the pursuit because he is bothered by asthma.”

Suspects who find themselves at the business end of a smoky vehicle spotters’ report are brought into an inspection center for testing. If tailpipe smoke exceeds government limits, the owners lose their vehicle license and must choose to either upgrade the vehicle or junk it.

Hong Kong’s unpaid smog spotters are faced with the daunting task of policing the region’s 588,000 vehicles. Of those vehicles, about 100,000 are diesel-fueled. In the first four months of 2010, the spotters hauled in 1,945 vehicles for testing.

That’s almost 2 percent of the city’s primary pollution producers that are either off the road or appropriately upgraded — in just one quarter of one year.