The health risks of microscopic air pollutants have been grossly underestimated on the mainland, with nearly 8,600 premature deaths expected this year in four major cities, a study has revealed. And premature deaths are "just a tiny fraction" of the adverse health impacts of tiny airborne particles, less than 2.5 microns in diameter, known as fine particle matter 2.5 (PM2.5). The startling findings were included in a report by Greenpeace East Asia and Peking University's school of public health which, for the first time, focused on PM2.5 health hazards in urban areas. Environmentalists have hailed the study, released yesterday, as ground-breaking, with data linking poor air quality to deadly diseases. Noting that the World Bank once put the number of premature deaths on the mainland as a result of air pollution at more than 200,000, Professor Pan Xiaochuan, of Peking University, said the study focused on a single pollutant and had not taken into account the long-term health impact of PM2.5, which could be far more dangerous. The study's estimation of combined economic losses caused by premature deaths, put at 6.8 billion yuan (HK$8.34 billion), was also likely to be far lower than the real figure owing to limited access to official statistics, he added. Fine particles have long been known to pose greater health risks than more than a dozen other air pollutants. They damage lung tissue and the cardiovascular system, cause lung cancer and other deadly diseases, and lead to a higher mortality rate. Based on official mortality figures in 2010 and limited PM2.5 monitoring data in Beijing, Shanghai, Guangzhou and Xian, mostly from environment-related research institutes, the study showed a more than 10 per cent rise in premature deaths caused by PM2.5 pollution in the four cities over the past two years. More than two-thirds of the 8,572 premature deaths this year caused by the microscopic pollutant occurred in Beijing and Shanghai. Although Beijing's air pollution problem was worse, Shanghai saw the most deaths linked to PM2.5 - 3,317. Pan said the study, which used internationally accepted mathematical methods, closely resembled the trends found in many other countries. "People living in less polluted areas appear to be more sensitive to poor air quality and more prone to pollution-induced diseases," he said yesterday. Pan and Greenpeace campaigner Zhou Rong, both of whom helped draft the report, said their estimated death tolls may be far lower than the real figures because of a lack of transparency on air pollution and health data. "We've tried to find more pollution readings and statistics about deadly, chronic diseases caused by long-term exposure to PM2.5, but we have made little progress," Zhou said. Previous research, partly sponsored by the government and released in 2006, showed that about 358,000 residents in 600 mainland cities died prematurely in 2004 from breathing polluted air, with an estimated health cost of 152.7 billion yuan. Although the central government has included PM2.5 in pollution parameters and unveiled a timetable for the mandatory release of PM2.5 monitoring data, Zhou said it was too little, too late. "PM2.5 is putting public health at high risk every day, but worse still, if we follow the current official plans [on tackling air pollution] we would need to wait another 20 years to meet the national standard, which remains too risky compared to the WHO guidelines," Zhou said. "Who can afford to wait?" The report said premature deaths would be cut by at least 81 per cent and economic losses at the four cities alone could be reduced by 5.5 billion yuan if stricter World Health Organisation standards were adopted.