PEDESTRIANS vainly covering their faces with their hands at traffic junctions have known for years that pollution is unpleasant. But precious little was ever done about it. Many will not have made any connection between dirty air and the health of their families. Most Hong Kong people are still at the first stage of pollution awareness: understanding that pollution looks and smells bad, but not realising its real impact. Even those who have made the empirical observation that what smells bad and makes breathing uncomfortable is likely to be bad for them, have had little more than the evidence of their senses to back their hunch. Now Hong Kong University has provided scientific evidence that controls imposed on factory sulphur emissions three years ago have dramatically improved child health in the industrial district of Kwai Tsing. It estimates up to 18,000 fewer visits were made to medical clinics as a result of cleaner air and the incidence of coughing, wheezing sore throats and other ailments has plummeted. Although children who lived with smokers remained far more at risk than their classmates, their health also improved in line with the general trend. The hope must be that this first local study will raise the level of public awareness and put pressure on government and industry to clean up their operations. The key is for the Environmental Protection Department (EPD) to drive home the message with a publicity campaign on children's health. It could back the local study with recent British findings that people living near busy roads are more likely to experience ill-health. A two-year Lancaster University project found a 17 per cent increase in headaches and lack of energy and a 14 per cent rise in coughs and breathing difficulties if traffic flows on nearby roads increased from 5,000 to 50,000 vehicles a day. Informed public opinion is a vital lever in the department's campaign to control vehicle emissions, especially to encourage a switch to petrol from high-sulphur diesel fuels. Hong Kong's health depends on getting the message across - and on the people demanding action.