Guangdong's air quality rated as good despite poor visibility Severe haze blanketing Guangdong in the past few days has exposed flaws in the mainland's air quality assessment system, a weather expert said yesterday. The flaws became apparent when the Guangdong Meteorological Bureau issued a haze alert on Wednesday afternoon about serious air pollution, but the provincial environmental authority's air pollution index (API) indicated there was no problem. The haze persisted throughout Guangdong yesterday, especially in Guangzhou, where visibility was just 6km in the morning. The haze reached its peak yesterday afternoon, prompting the meteorological bureau to issue a haze alert for Guangzhou, where the visibility was less than 5km. It was the first time the bureau had released such a warning since the alert system was set up in June. 'The alert indicated the air pollution was quite serious at that time,' bureau meteorologist Wu Dui said. 'If that wasn't the case, we wouldn't have sent the alert out.' But according to the Guangdong Environmental Protection Bureau, yesterday's API reading for Guangzhou was only 79, indicating air quality was still 'good'. An API reading of 100 to 200 means the air is 'lightly polluted', while readings between 200 and 300 indicate 'moderate pollution' and those above 300 point to 'serious pollution', according to the mainland's air quality assessment system. Some residents complained yesterday about the difference between the two systems over the past few days. 'The pollution should be quite serious because I had problems breathing as I walked home,' Tianhe district worker Zhang Shuai said. 'How dare the TV news tell us the air quality was good.' Professor Wu said the difference between the two reports revealed that the national API system was not accurate enough to assess air quality because it took only three major pollutants into account. He said the API system was established in the 1970s and was based on readings of three major air pollutants: sulfur dioxide (SO2), nitrogen dioxide (NO2) and particulate matter with a median diameter less than 10 microns (PM10). The index was not accurate enough because some other major pollutants blanketing the Pearl River Delta region were not taken into account and many airborne particulates were too small to be accurately assessed by the system. Many other countries and regions based their air quality calculations on readings for at least five pollutants and included levels of much smaller airborne particulates harmful to humans, with some foreign countries adopting a more accurate standard, PM2.5, to evaluate the pollution from airborne particulates. 'Changes to the API system have lagged behind changes in air pollution,' Professor Wu said. 'That's why we established such a haze alert system in the region.'