Hong Kong's new air quality health index shows changes at four out of nine monitoring stations
But more moderate gradings of pollutants does not mean new system is less stringent
Air quality recordings released yesterday after a trial run of the government's new index at its nine monitoring stations showed that three "highs" under the old system had become "moderate" under the new one.
One recording turned from "high" to "very high". Recordings at the other five stations were "very high" or "high" under both indices. But environmentalists said this did not mean that the new index, the air quality health index (AQHI), was less stringent than the old one - the air pollution index (API).
"In fact, it reflects the health risk the pollution brings to the public more accurately," said Melonie Chau Yuet-cheung, senior environmental affairs officer with Friends of the Earth.
Introduced in 1995, the API converts air pollution data into a value ranging from 0 to 500, putting it under five bands from "low" to "severe".
Experts say the AQHI, which will be officially launched on Monday, will offer the public better, clearer and more timely advice on health risks than the present system.
It calculates the hospital admission risks brought about by air pollutants. There are 10 bands under this new index. They consist of five categories from "low" to "serious".
The old index reflects the intensity of air pollution, which means the recordings refer to the "air pollution level". However, the new index indicates the health risk arising from pollution, and the recordings therefore reflect the "health risk level".
Results from the trial run showed that the 5pm readings for Eastern district, Kwun Tong and Tai Po were "high" under the API, suggesting that there was no need for the public to take immediate action. The readings for the three became "moderate" under the AQHI, again meaning that no immediate action was needed.
Meanwhile, the reading for Yuen Long turned from "high" to "very high" under the AQHI. In this case the new index advises the public to reduce outdoor activities, while the old one does not.
Chau welcomed the new index as it can better reflect the health risk of air pollution.
"API calculates the intensity of five air pollutants. It means that if only one of the five pollutants is exceptionally high, the reading will come out high," Chau said. "But the thing is, in order for the pollution to be harmful to your health, we need to consider the combination of the five pollutants. The new index was structured in a way to achieve this."
But Chau said one problem with the new index was that it still did not stipulate that government departments must take certain measures such as banning cars from the streets when pollution was severe.
This was a measure that Beijing had already taken and Hong Kong should consider, she added.
Roy Tam Hoi-pong, chairman of Green Sense, also welcomed the new index as it measures PM2.5 - tiny particles that are particularly hazardous to health - which were not calculated under the old API.
After the public had taken some time to get used to the new index, he said, the government should consider making it mandatory to suspend school classes if pollution hits the worst level.
Watch: How to deal with Hong Kong's smog