THE air pollution index announced by the Government yesterday has been criticised by experts before it can be launched. The index, which begins on June 6, will measure and tabulate rooftop air pollution levels at monitoring stations throughout the territory. But it ignores street-level air pollution readings from the road-side Mongkok monitoring station which produces higher readings than the rooftop sites. The Environmental Protection Department maintains it is correct to choose rooftop readings over street level because most people spend their time in buildings, said principal environmental protection officer Tse Chin-wan. But Dennis Leung Yiu-cheong, a lecturer in air pollution at Hong Kong University's Department of Mechanical Engineering said: 'This is not a realistic picture without the inclusion of street-level readings. 'Without the inclusion of street readings from areas like Mongkok and Causeway Bay the index does little.' The director of the Institute of Environmental Studies at the University of Science and Technology, Professor Gary Heinke, said an index that only raised awareness lacked teeth. 'It perhaps only quantifies what people generally believe to be the case,' he said. The index divides air quality into four categories - good, moderate, unhealthy, and very unhealthy. No public action is required for a 'good' or 'moderate' reading. An 'unhealthy' reading indicates people with existing heart or respiratory illness should reduce activity and healthy people may feel some discomfort. The 'very unhealthy' alert means even the general public should reduce exercise and stay indoors. Headteachers are instructed to keep children inside during recess on risky days. From 1990 to 1994, the number of days that fell in the unhealthy category was 29 in the industrial area, 25 in the urban area. No 'very unhealthy' days were recorded. But the Government admitted it had no plans to close down factories or restrict vehicle use during high pollution counts. It was up to the public to stop exercising and stay indoors when the air index rises. Legislator Christine Loh Kung-wai said: 'This is like the cholera and hepatitis outbreaks when the Government's solution was to tell us to cook our food better. 'Now they are saying 'don't breathe so hard', which is just an excuse for inaction.' Government figures predict air pollution will increase by 50 per cent by the end of the decade. But the daily and monthly readings show very few days which exceed the air quality objective standards. 'On a long-term basis we have a problem,' senior environmental protection officer Pang Sik-wing said. 'But the daily indicator is a standard for short-term exposure.'