Regional warming in East Asia over the past 30 years has led to a rapid rise in surface ozone pollution that may have led to thousands of premature deaths a year, a Chinese University study found. The researchers warn the situation is likely to get worse as fossil fuel emissions increase. Ozone is formed by volatile organic compounds (VOCs) reacting with nitrogen oxides (NOx) from sources such as vehicles. The pollutant can cause breathing problems and serious lung disease. The study found that summertime temperatures in mainland China and surrounding regions had risen by up to 3 degrees Celsius over the past three decades, intensifying ozone in the lower atmosphere by 2 to 10 parts per billion by volume (ppbv). This increase was associated with an estimated 5,600 extra premature respiratory deaths per year in East Asia - which includes mainland China and Hong Kong - between 1980 and 2010. But Professor Amos Tai Pui-kuen of the university's earth system science programme said increases in human-induced emissions from fossil fuel burning had raised ozone levels to 25ppbv over this period, which may have caused an extra 65,000 ozone-related premature deaths per year. "Our results show that warming in China, indeed, might have exacerbated air pollution further over the past few decades and had a direct impact on human health," said Tai. "If we include the health impact of more frequent heat extremes, such as heatstroke, the real costs of climate change might have been even higher." The 18-month study analysed historical weather and satellite observations of land cover in computer modelling that simulated atmospheric chemistry and pollutant formation. Tai said warmer temperatures and carbon dioxide increased the growth of vegetation. Trees and plants emit VOCs naturally and these react with NOx emissions from vehicles and power plants, creating yet more ozone. "South China and Hong Kong will likely experience more serious ozone pollution due to the 'double impact' of climate change and enhanced vegetation growth in the future if background nitrogen oxides from industrial [sources] and vehicles remain high." Tai urged regional governments to reduce NOx emissions, especially from vehicles, and to take into account future warming and land use changes in the greater Pearl River Delta region. Clean Air Network campaign manager Patrick Fung Kin-wai said the findings were in line with his own group's research, which last year found that ozone pollution in Hong Kong had hit a historic high. VOC emissions in the delta region have long been a problem and even with the Chinese economy slowing, there were no signs of it coming down yet, he said. According to the Environmental Protection Department, ozone concentrations measured at the city's air quality monitoring stations have increased by 25 per cent over the past five years. Hong Kong and other cities in the Pearl River Delta have pledged to reduce VOC emissions by 15 to 25 per cent by 2020 from 2010 levels.