The government has been urged to improve air quality after a Chinese University study showed that air pollution significantly increased hospital admissions for asthma patients. Researchers from the university's departments of medicine and therapeutics and community and family medicine reviewed the relationship between hospital admissions for asthma at 15 major public hospitals and the concentration of pollutants in Hong Kong from 2000 to 2005. The study found that when the concentration of ozone increased 10 micrograms per cubic metre, the overall risk of hospital admissions for asthma increased 3.4 per cent, and when nitrogen dioxide concentrations rose by the same proportion admission risk rose by 2.8 per cent. An increase of particulates of 10 micrograms per cubic metre sent the admission risk up by about 2 per cent. And children, comprising newborns to 14-year-olds, tended to be more at risk from pollutant increases than those aged 15 or above. 'Asthma is an airway disease involving the respiratory system in which the airway constricts and becomes inflamed. Poor air quality can irritate the airway and cause shortness of breath,' David Hui Shu-cheong, the head of the university's division of respiratory medicine, said. But the researchers did not find a link between the air pollution index and the admission risk because the index measured a basket of different components, he said. Between 2000 and 2005, about 32 people a day on average were admitted to public hospitals for asthma. There were more admissions in winter, about 35 a day on average, when the temperature was below 20 degrees Celsius. In total, 69,716 admissions for asthma were recorded between 2000 and 2005. The researchers said the number was more or less the same each year. Usually, an asthma patient stayed in hospital for five to seven days. 'The government should work harder to improve the air quality. In our research, ozone was the most important air pollutant associated with increased hospitalisation admissions for asthma. An alert system for when the ozone concentration is high should be considered,' community and family medicine professor Wong Tze-wai said. Professor Wong said the concentration of ozone was sometimes higher in the countryside because there were fewer particulates in the air to refract away part of the ozone. On the other hand, there were generally fewer other pollutants. In previous studies, the prevalence of asthma in children aged six to seven and 13 to 14 was 9.4 per cent, while for people aged over 70 it was 5.8 per cent in Hong Kong.