Yet another study has confirmed that air pollution is taking its toll on people's health - this time on patients with a smoking history. Public hospitals admitted 75 patients suffering from chronic lung disease on an average winter day, 10 more than the daily average of 65 over a five-year period, due to higher concentrations of pollutants in cold air, according to a study released by the Chinese University yesterday. The study, conducted by the university's faculty of medicine, is drawn from data collected from 15 major hospitals under the Hospital Authority. Nearly 120,000 admissions for chronic obstructive pulmonary disease were recorded between January 2000 and December 2004. Ozone was the biggest factor in people needing to go to hospital. When the average temperature was below 20 degrees Celsius, the mean daily levels of nitrogen dioxide and particulates were comparatively higher, according to the findings. One of the researchers, Wong Tze-wai, suggested patients with lung diseases should avoid going out in cold weather when the air pollution level was high and the wind was weak. 'These are the times when pollutants come at high concentration in the air,' he said. His research partner, Fanny Ko Wai-san, meanwhile, urged the government to immediately take measures to improve air quality in the city. David Hui Shu-cheong, head of respiratory medicine, observed that 95 per cent of patients had smoked for many years before being diagnosed with the disease. Leung Ming-choi, 70, a chronic obstructive pulmonary disease sufferer and former smoker, said he had problems breathing when the air became polluted. 'The worse the air quality, the harder I have to breathe,' said Mr Leung, who has been in hospital three times since 2002. 'I have to inhale the bronchodilator more often when it is very polluted. 'I can walk for over an hour when the air is clean, but much shorter when it is filthy.' In 2004 alone, chronic obstructive pulmonary disease, which includes disorders such as emphysema and chronic bronchitis, caused 2,123 deaths in Hong Kong, making it the city's fifth biggest killer. The World Health Organisation said in October that air pollution was estimated to cause about 2 million premature deaths worldwide per year.