Guangdong cities on list of filthy Air quality in the Pearl River Delta is some of the filthiest on the mainland, with the number of smoggy days recorded in Shenzhen and Dongguan shooting up last year. Shenzhen recorded 231 smoggy days, a sharp increase from 164 in 2006, the lead story in the Southern Weekend newspaper said yesterday. Dongguan, one of the top industrial cities in Guangdong and home to many Hong Kong factories, was now the dirtiest city in the province in terms of air pollution, the newspaper said. Quoting a report by meteorological experts in Beijing and Guangzhou, the newspaper included delta cities, especially those west of the Pearl River mouth, on a list of mainland cities suffering from the worst smog recorded across the country. The cities span the most developed regions, including Beijing, Shanghai, Xian, Chengdu, Taiyuan and Shenyang, Nanjing and Hangzhou. The report came after Premier Wen Jiabao declared an initial victory in curbing pollution last year. It has sparked doubts about the effectiveness of pollution controls which cost billions of yuan annually. About 358,000 urban dwellers in 600 mainland cities died prematurely from breathing polluted air in 2004, said the report from the Chinese Academy of Environmental Planning under the newly upgraded Ministry of Environmental Protection. Health costs from premature deaths and serious illness associated with air pollution were estimated at 152.7 billion yuan in 2004. Academy chief engineer Wang Jinnan said Hong Kong had been hit hard by the worsening pollution. The Guangdong Meteorological Bureau said earlier that 27 major cities and counties in the province, including Guangzhou, had experienced the worst smog last year in the 59 years records had been kept. The provincial capital recorded 75.5 smoggy days last year, with 22 days in December alone. Bureau atmospheric scientist Wu Dui told the newspaper that mainland pollution standards, which measured only three main air pollutants - sulfur dioxide, nitrogen dioxide and particulate matter with a median diameter less than 10 microns - were partly to blame for appalling pollution and mounting health risks. Most industrial countries and the World Health Organisation believe PM2.5, which refers to particulate matter with a median diameter less than 2.5 microns, is a more accurate standard for evaluating airborne pollution. Particulate matter from the burning of fossil and other types of fuels, is the main pollutant in most mainland cities. The academy's Professor Wang said progress reported by the government may not accurately reflect real air pollution. He said it would take years before the country could start measuring the much smaller particulate matter, believed to be the real cause of deaths, as only big cities like Beijing and Guangzhou had the technology. Hong Kong has just experienced the smoggiest March since 2004. The Hong Kong Observatory recorded 137 hours of reduced visibility during the month. Despite various anti-pollution measures introduced last year, the city's air pollution reading in 2007 was also the worst since 2004, with 87 days when the air pollution index (API) registered over 100. Last year, there were 74 days with high API readings recorded, compared to 49 days in 2005 and 56 days in 2006.