Hong Kong's Ombudsman is probing why the city has not changed its air quality standards since the late 1980s despite increasingly vocal criticism of pollution in the global financial hub.
The watchdog has sent a letter to the territory's government asking for an explanation of its outdated air quality objectives, said Thomas Choi, a senior environmental affairs officer at Friends of the Earth Hong Kong.
"The government has said it would update the (Air Quality Objectives), but nothing has happened," he told AFP on Tuesday.
Choi said the watchdog's probe would last between three and six months, although its findings are non-binding.
The Ombudsman's office - which acted on a complaint filed by Choi - declined comment Tuesday, citing privacy laws.
The investigation comes as Hong Kong is set to record its worst-ever year for roadside air quality, according to government figures for 2010, sparking renewed calls for action on the hot-button public health issue.
Emissions from the factory belt in southern China, which seep over Hong Kong's border, combined with local emissions from power plants and transport, have generated a thick blanket of haze over the teeming metropolis in recent years.
New air quality standards in line with World Health Organization recommendations were presented to the city's Legislative Council last summer, the first update since 1987, but no further action has been taken, Choi said.
The city's Environmental Protection Department said it had received the ombudsman's letter, but declined to comment on Choi's complaint.
"Similar to the handling of any other complaints to the Ombudsman about air pollution, we would cooperate with the Ombudsman by providing the necessary information but would not comment on individual cases," it said in statement e-mailed to AFP on Tuesday.
The department added that it was "considering carefully the relevant policy aspects and implementation details with an aim to find the best way forward".
A survey released last month by public policy think tank Civic Exchange found one-quarter of residents would like to leave Hong Kong to escape its pollution.
Green groups say authorities' efforts to combat the problem - including fitting old buses with emissions-busting devices - fall woefully short.