Despite setting clean air targets, the city's smog problems have been increasing every year, and authorities have finally brought in measures to ban the highest-polluting vehicles.
Diesel particulate matter is a major component of smog, and is a concern for many cities around the world where old-technology models still roam in large numbers.
Up to 40 percent of the commercial vehicles in Hong Kong only meet the European 'Euro II' emissions standards--a restriction that allows for 12.5 times more particulate matter than current Euro V standards.
Vehicles meeting that standard also produce greater carbon monoxide, hydrocarbons and oxides of nitrogen, all of which also contribute to smog. Euro II was replaced in Europe over a decade ago.
The ban comes after 15 years of clean air measures which haven't reduced the city's smog.
The pollution is said to be responsible for 3,000 premature deaths per year, and air quality has been in decline since 2007. Last year saw 175 days of "high" pollution--more than twice that of 2007.
Hong Kong will offer subsidies for cleaner transport, aimed at helping those whose vehicles are being banned to continue as normal. Officials have promised to use a "bigger stick" to coerce people into cleaner vehicles.
Other measures to reduce pollution include improving the index to gauge air quality, and reducing bus routes.
A new set of air quality objectives will be introduced by 2014, and the city's targets are within reach by 2020.