Hong Kong's leading authority on air quality said Thursday he is leaving the city to avoid its polluted air and keep his respiratory problems under control.

Anthony Hedley, who created the Hedley Environmental Index, which tracks the public health and economic costs of Hong Kong air pollution in real time, is relocating to the Isle of Man off the west coast of Britain.

"I need to reduce my exposure to polluted air because I know from experience that my respiratory symptoms subside quickly when I am in cleaner air," the 69-year-old Briton told AFP.

"Because of my medical history I now want to avoid the biological stress which comes directly from breathing the polluted air in Hong Kong."

Hedley said he had beaten cancer but was now confronted with respiratory symptoms such as cough and phlegm, which he said were aggravated by the poor air quality in the financial hub.

He said he will continue to work with his colleagues at the University of Hong Kong's Community Medicine Department, but mainly electronically.

A government spokesman said it was a losing one of its "good comrades on combating air pollution".

"To combat our and regional air pollution, we have been taking a two-pronged strategy to cut emissions from local sources and work closely with our neighbouring cities," the spokesman added.

Over the past two decades, Hedley has campaigned for radical measures to control emissions of air pollutants from road traffic, shipping and power plants.

But he said he was disheartened by what he said was the government's slow progress in tackling the city's top environmental problem.

"One of my biggest regrets is that we have not been able to move the issue," he said.

Statistics from the Hong Kong Observatory show that the annual number of hours of "reduced visibility" - one of Hedley's key research areas - rose from 295 in 1988 to 1,139 in 2009.

The term refers to visibility of less than eight kilometres (five miles) in the absence of fog, mist or rain.

The emissions from Hong Kong's factory belt in the neighbouring Pearl River Delta also contributed to the pollution.

Clean Air Network, an environmental NGO, said in a statement following Hedley's announcement: "It is indeed a sad irony that one of those most committed to alleviating Hong Kong's air pollution now has to leave the city primarily for that reason."