Green groups have welcomed the launch of real-time reporting on fine suspended particulates that are a leading component of smog.
But they said Hong Kong is merely aping a similar nationwide monitoring plan announced by Beijing last week.
The Environmental Protection Department yesterday began regular monitoring of the tiny floating particles that are also known as PM2.5, or which measure 2.5 micrometers in diameter or less.
Monitoring of PM2.5 levels has been carried out at three stations since 2005, but the readings were not publicized.
A department spokesman said all stations will now monitor these levels in anticipation of moves to expand the scope of air-quality monitoring.
The stations - comprising 11 general stations and three roadside stations - will now reveal PM2.5 concentrations in the air on an hourly basis.
Environmentalists said the plan is a step in the right direction but accuse the government of merely falling in line with Beijing, which began monitoring PM2.5 levels last week.
"It is disappointing that Hong Kong, which used to be the leader in environmental issues, is now simply following in the footsteps of China," said Mike Kilburn, head of environmental strategy at the Civic Exchange.
Clean Air Network senior campaigner Erica Chan Fong-yin said the plan is an indication that the territory is now paying more attention to quality rather than quantity.
But Chan said doubts still remain over monitoring accuracy because all general stations are five meters above ground.