What's going on?

Just days after the American Chamber of Commerce rolled out a gloomy report reminding Hong Kong of an air- pollution-spurred exodus of American executives, the skies this week have been suddenly and unusually clear.

As Hong Kongers were making their afternoon commute home Tuesday, anyone looking out from the Hong Kong Observatory in Tsim Sha Tsui or Hong Kong International Airport on Lantau Island would have been able to see about 30 kilometers into the distance.

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"Those are considered very good visibility readings," said a spokesman for the observatory. He explained that any visibility of 8km or less was considered "low."

"These clear skies are great," said Hong Kong University of Science and Technology environmental professor William Barron. "They remind us of what we should be seeing all the time."

Throughout the day, air-pollution stations scattered throughout Hong Kong registered low readings, with the Environmental Protection Department, which monitors the pollution index, reporting the numbers at roadside stations in Central and Mong Kok - usually Hong Kong's worst locations - at "medium" levels of 40 and 43 apiece. The worst result came in Causeway Bay, where the reading hit 55.

A reading of 100 or higher is considered "very high" by the department.

Earlier this summer, the government launched the Action Blue Sky Campaign as a key initiative to combat the city's pollution woes.

The plan includes calling on people to turn down their air conditioners and conserve electricity.

But Gloria Chang Wan-ki, a campaigner with Greenpeace Hong Kong, chalked up the recent improvement in air quality to Hong Kong's historically clear summers - not any government action.

She said meteorological factors, such as wind direction - whether from the factories in Guangdong province or from the South China Sea - were far more vital to the recent spate of blue skies than any government action to decrease air pollutants.

The government should be paying attention to the American Chamber's report this week which, she said, reflected what the public really thought of the local conditions. "The report shows how uncomfortable and dissatisfied people are with the air-quality situation in Hong Kong," she said.

Professor Barron said that by historical standards, even the usually clear summers were getting worse.

"Ten years ago, we had this kind of sky every summer, all summer," he said. But a recent spike in typhoon activity in the South China Sea has strengthened wind activity, which makes even the good patches of weather fleeting and ephemeral. "I hope these occasional few days are a reminder of what we've lost," he said.

According to the hour-by-hour data compiled by the government, the worst day this month came on the evening of August 9 when roadside readings in Central, Mong Kok and Causeway Bay reached 131, 126 and 147.

Since then, the air quality has remained under 100, except for one brief period when readings hovered slightly over 100. The worst month so far this year has been February.

The clear days may be fleeting but, politically speaking, the blue skies could have an important impact on public perceptions of the effectiveness of the government's measures.

Chang, however, was quick to rebut that. "The government has not taken bold measures to tighten up emissions standards," she said, characterizing the current campaign as "lip service and hot air."

She pointed to government figures showing an increase in the emission levels of sulfur dioxide and particulates over the past few years.

According to the Environmental Protection Department, sulfur dioxide emissions have risen steadily in recent years, from 56,300 tons in 1999 to 94,800 tons in 2004.

The same trend, though less marked, can be seen for particulate matters.

"This kind of data cannot be ignored," Chang said. "Facts are louder than just perceptions."

And even good perceptions of improving air conditions, Barron said, may not last long.

"Don't count on this," Barron said. "It's only going to last as long as the wind is blowing from the south and the east."