Drivers of cars and vans that breach emission standards face having their vehicle licences revoked if caught under a HK$12 million detection scheme to be introduced in September.
More than 42,000 private vehicles, taxis and minibuses will come under closer on-street monitoring by remote sensing technology using infrared or ultraviolet rays to measure the emitted pollutants.
Owners of vehicles that breach the standard will have 12 days to fix them. If they don't, their licences will be revoked by the Transport Department.
Introducing the scheme yesterday, assistant director of environmental protection Mok Wai-chuen said the scheme was aimed at petrol-fuelled cars and liquefied petroleum gas-driven vehicles like taxis and minibuses.
He said that while polluting diesel vehicles could be seen spewing black smoke, this did not work on taxis and minibuses with different fuel.
"We have been using the technology since 1993 and we are fully confident of its reliability as there is a lot of supporting scientific data," he said.
Officials will place three sets of mobile equipment - a camera and two remote sensing machines - at three different locations each day.
If both machines record emissions from a passing vehicle that are more than double the emission standard in force when the car was new, the drivers will be told to drive their cars to designated centres for a test that will cost them HK$310.
Mok said Hong Kong's roadside air pollution was unique in that excessive emission of nitrogen oxides from vehicles could react with the regional ozone pollution and lead to a high concentration of nitrogen dioxide.
Since 1999, nitrogen dioxide emissions by the roadside have risen 21 per cent while other pollutants like sulphur dioxide and fine particulates fell.
Mok said taxis and minibuses were the main culprits as they ran for long hours. Poor maintenance or failure to replace pollution-reduction devices like catalytic converters would greatly aggravate pollution, he said.
The government has spent HK$180 million to subsidise the replacement of catalytic converters in taxis and minibuses.
Mok said it was now the responsibility of the drivers to maintain their vehicles properly to meet emission standards.
Kwong Sum-yin, chief executive of the Clean Air Network, welcomed the scheme but urged the government to roll out mandatory testing schemes for all polluting commercial vehicles.
Hong Kong choked on its smoggiest day of the year so far on Sunday with pollution that represented a "serious risk" to health. All but two general stations and all of the roadside stations were at level 10+, the highest level on the government's Air Quality Health Index.