Researchers have singled out eight urban roads - most of which are not monitored by the government's air-quality network - as Hong Kong's most polluted thoroughfares.
The roads have nitrogen dioxide readings of up to 300 micrograms per cubic metre of air, categorised as 'very high' on the government scale.
Professors from the University of Science and Technology, in a study sponsored by the Jockey Club and supported by the think tank Civic Exchange, also found the eight roads far dirtier than two highways with far more traffic but better ventilation.
The information - released as the Environmental Protection Department is due to report progress of a review of air quality objectives to lawmakers on Monday - was collected with a mobile system the researchers and think tank said should be added to the network of fixed sites.
Using a specially equipped van, the team travelled through busy roads of all 18 districts from September last year to April. It spent four days on each district and measured each chosen road at least eight times, during and outside rush hours, to get an average.
They found high roadside pollution levels were not restricted to Central, Mong Kok and Causeway Bay, which the department monitors with fixed stations, but also existed in Kwun Tong, Hung Hom, Wan Chai, Kwai Chung and Eastern district.
Concentrations of nitrogen dioxide exceeded 300 on King's Road and Ma Tau Wai Road, which are not officially monitored, as well as Hennessy Road, Des Voeux Road Central and Nathan Road, parts of which are covered by the department's network.