LAST Sunday was bad for Hong Kong's health. The collapse and eventual death of three hikers in three different places may have been the first sign that air pollution is more than a nuisance - it is lethal. 'Heatstroke is mostly a genetic problem - there's a genetic predisposition to overheating, going into organ failure and dying. But presumably the pollution could contribute to the deaths,' said Dr Adrian Wu of the University of Hong Kong's department of medicine, and a specialist in diseases caused by allergies, such as asthma and allergic rhinitis. 'It was a very hot day and the pollution had a blanketing effect,' he said. Neither Dr Wu, nor anyone else, is suggesting air pollution on its own killed those people. But he explained that the 'blanketing' effect, the way polluted air holds heat in the air and coats our skin pores so we cannot sweat effectively to cool ourselves down, could have made those people's body temperatures rise to fatal levels. In 1998 there was only one recorded death from heatstroke. This is partly explained, Hospital Authority spokesman Anita Mau said, by the fact that 'our clinicians have a strict definition of heatstroke'. Even so, three deaths on one day seem excessive, especially as 14 others had to be rescued from exposed areas by helicopter. And when that day was not only hot but also heavily polluted, suspicions inevitably rise. Raymond Leung Pak-ming, principal environmental protection officer at the Environmental Protection Department, has never come across cases of air pollution contributing to heatstroke. But studies he quotes from the last couple of years by the University of Hong Kong and the Chinese University show how dangerous last Sunday was. There is, for instance, a clear association between high levels of nitrogen oxide and ozone levels in the air and deaths from heart and lung disease. Last Sunday, both levels were high. A peak air pollution reading of 124 was recorded at Tung Chung; anything more than 100 means the young, very old and frail should stay indoors. The first study, by the Chinese University of Hong Kong's Department of Community and Family Medicine, looked at deaths and hospital admissions for heart and lung diseases in 1994-1995, and assessed whether higher pollution days were a factor. They found that when levels of any of the major pollutants - nitrogen oxide, sulphur dioxide, ozone and particulates - were high, more people developed such severe lung or heart disease that they needed to be admitted to hospital. When ozone levels were high, more people died of lung diseases such as asthma and bronchitis, and of circulatory diseases like heart attacks and strokes. When nitrogen oxide levels were high, more lung disease-related deaths occurred. A later study by the Department of Community Medicine at the University of Hong Kong, covering 1995, 1996 and the first half of 1997 came up with similar results. In this study, higher levels of nitrogen dioxide and ozone 'were positively associated with [hospital deaths from] circulatory [strokes and heart attacks] and respiratory [lung] diseases'. Health Department figures show a dramatic rise in disease made worse by pollution. In 1997 the number of people admitted for all forms of bronchitis was 6,873. In 1992, the number was 2,811. The costs associated with this pollution-induced illness have been estimated at $3.8 billion per year. The studies and statistics only cover the years up to 1997. Since then, pollution, especially that caused by nitrogen dioxide and ozone has worsened. It seems extraordinary, given such clear evidence that the inaction on air pollution is killing us, that people are not taking to the streets and demanding a solution to what may spell the end for Hong Kong. Part of the reason is because most of those deaths occur in intensive care units and emergency wards to patients with weak hearts, the elderly who have suffered from chest problems for years, and diabetics who have been in and out of hospital. Pollution is also helping kill children and young teenagers with asthma, an illness complicated by pollution. Every year almost 100 people die of asthma in Hong Kong, and many of these are teenagers and young adults. Hong Kong has the highest rate of childhood asthma in Asia. Another reason many of us are not truly aware of the danger Hong Kong's air poses is we do not know exactly what is in the air and what it is doing to us. Air pollution is complex and is made up of a number of components. These differ from city to city depending on whether it is unregulated industry, power generation, motor vehicles or dust-causing industries like construction that cause the problem. The main components of Hong Kong's air pollution are black smoke, nitrogen dioxide, total suspended particulates of which respirable suspended particulates are the health-endangering fraction, ozone, sulphur dioxide, carbon monoxide, and volatile organic compounds. Of these nitrogen dioxide and ozone are the cause of most problems and are associated with higher rates of death. But respirable suspended particulates, which as a part of the total suspended particulates group that causes the dirty mist we see in summer, also put more people in hospital. Ozone at lower levels, which is formed by the effect of the sun on polluted air, especially nitrogen oxide, attacks the nose, throat and breathing passages. The burning, watery eyes, and sharp pains in the throat and chest you feel as you breathe in tell you there is a lot of ozone in the air. Nitrogen oxide irritates the lungs and lowers resistance to lung and throat infections such as influenza. People who find they cannot shake off viral infections are feeling the effect of nitrogen dioxide on their lungs. Those with existing lung problems like asthma can be tipped into suffering an acute attack or developing a serious infection if they breathe in too much. It is also believed that nitrogen oxide can impair the development of children's lungs, leaving them with reduced breathing capacity and greater susceptibility to infections and asthma. In Hong Kong, while some politicians try to deflect blame on to industry in Guangdong, almost everyone working in the field agrees the problem and its solution lies with our poorly controlled transport sector. Even if vehicle engines improve we are still making it worse by building bigger and better roads able to carry more and more vehicles. Between 1991 and 1997 vehicle numbers have risen 30 per cent and better roads mean kilometres driven have risen 25 per cent. During the same time, the level of harmful pollutants produced by those vehicles has also risen. 'The way forward is pretty clear but taking the decisions is harder,' said Professor Anthony Hedley, of the University of Hong Kong's Department of Community Medicine. 'If they hauled all the smoky vehicles off the streets what a dramatic change it would make. 'Unless we get a much better transport policy quickly the whole thing will get much worse. The Transport Department is out of control.' Professor Hedley said the best transport option, extending the Mass Transit Railway and building light rail, is avoided as too difficult and expensive. And as demand for public transport rises in areas not serviced by the MTR, more and more buses are pulled into service. In Causeway Bay at five in the afternoon on any weekday, all the roads are jammed by mostly empty buses packed head to tail. It is no accident that Causeway Bay regularly records some of the worst roadside air pollution readings. As Professor Hedley points out, the administration has already proved that taking necessary decisions to improve air quality, and forcing industries to comply, can make a difference. In 1990, high sulphur fuels were banned and industries were forced to stop their use almost overnight. The fall in sulphate, a toxic component of air pollution, was dramatic. In industrial areas the level was cut by 80 per cent. The effect on the health of children in these areas was equally dramatic. Professor Hedley and colleagues assessed the lung status of schoolchildren in Kwai Chung and other areas and 'the prevalence of symptoms [such as coughing and wheezing] fell and their respiratory function improved', he said. Before the sulphate levels were reduced, children in industrial levels had high rates of 'bronchial responsiveness' a measure of the irritability of their breathing tubes, or bronchi. If someone already has a high level of bronchial responsiveness the arrival of another irritant likely to cause asthma such as mould, dust, pollen or cat fur will lead to asthma even in someone who would not normally suffer. After the sulphate levels were reduced, bronchial responsiveness returned to normal. Such quick action can make a difference. But as a government source sadly noted, 'it was so much easier then'. When air pollution levels are high, only people with known illness are warned to stay inside. Many of us assume because we are healthy, or think we are healthy, it is safe to venture outdoors. But we do so only at risk to ourselves.