Cities that adopt roadside emissions sensors to detect high polluting vehicles, together with an enforcement program to inspect and repair these vehicles, could significantly improve urban air quality, new research shows.

Vehicle emissions are the most significant source of air pollution in the urban environment worldwide, impacting the climate and the health of millions of people. Reducing air pollution is a key target of the United Nations sustainable development goals.

“Car exhaust fumes contain poisonous gasses such as carbon monoxide, nitrogen oxides, and particulate matter that cause lung cancer, heart failure, asthma and other diseases,” says research co-author, Professor John Zhou from the University of Technology Sydney (UTS).

“Remote sensing equipment uses a sensor and light beam to measure chemical concentrations in the exhaust as a vehicle drives past. A camera records the license plate, so vehicles can be identified for inspection and repair,” he says.

Although new cars are required to meet emissions standards, older cars, those with high kilometers and cars that have been modified, or not well maintained, can malfunction and have significantly higher emission levels, leading to high levels of air pollution.

Researchers from UTS partnered with the Hong Kong Environmental Protection Department (HKEPD) and the Hong Kong Vocational Training Council to evaluate the accuracy and effectiveness of Hong Kong’s remote sensing enforcement program.

They examined data from the start of the program in September 2014 to December 2018, which included around 2.9 million vehicle counts from over 150 monitoring sites. They also looked at air quality monitoring and chassis dynamometer testing data.

In total, 16,365 high-emitting LPG and petrol vehicles were identified by remote sensing and issued with emission test notices. Among them, 96.3% of the high emitters were successfully repaired and subsequently passed the Hong Kong Transient Emission Test (HKTET).

Only 1.4% of vehicles failed the HKTET, and 2.3% of vehicles did not take the test, causing the cancelation of 558 vehicle licenses.

The study, published in the journal Science Advances, found that Hong Kong’s remote sensing enforcement program led to a significant and continuing reduction in the level of harmful chemicals at the roadside and in the wider atmospheric environment.