China is mulling more stringent appraisal standards for air quality, and pilot projects are likely to start from coastal cities in the Yangtze River delta and Pearl River delta next year.
The environmental authorities are planning to include particles less than 2.5 microns (PM2.5) and ozone, into the Air Pollution Index (API), which currently measures the concentration of sulfur dioxide, nitrogen dioxide and PM10, or particles smaller than 10 microns.
The new evaluating system will cover all the airborne pollutants that are damaging to health as per the global air quality guidelines issued by the World Health Organization (WHO) in 2005.
Currently, 113 key cities tasked with environmental protection publish daily reports on the API results. A day is determined as a "blue-sky day" when the API falls under 100, which means air quality is generally good.
In recent years, however, cities are beginning to suffer from poor visibility more often, even when the API result suggests that the air quality is good.
This is being caused by the worsening haze and ozone pollution in some major cities in eastern China, according to Wang Jian, an official from the pollution prevention department under the Ministry of Environmental Protection (MEP).
Shanghai registered a total of 167 and 143 hazy days in 2006 and 2007, respectively. Last year, Guangzhou and Shenzhen also saw 110 and 142 hazy days, respectively.
"PM2.5 is to blame for the haze," said Wang. "Vehicle exhausts that contain black carbon, sulfates and nitrates contribute a lot to the density of PM2.5, which is more damaging to the respiratory system than PM10."
Ozone at the ground level, which is formed when hydrocarbons and nitrogen oxides (NOx) combine in the presence of sunlight, causes photochemical smog and also harms people's health.
Several major cities, including Beijing, Shanghai, Guangzhou and Shenzhen, are already monitoring PM2.5, said a researcher surnamed Li from the China National Environmental Monitoring Center.
Last year, pilot projects on ozone monitoring were carried out in cities that hosted the Beijing Olympic Games. Apart from the capital itself, these included Shanghai, Tianjin, Qingdao, Shenyang and Qinhuangdao.
A universal appraisal standard for the two additional pollutants is still missing.
"Standards for the two pollutants used in Europe and the US will be used for reference," Li said. "And it is likely that China will start with less stringent standards, and move towards stricter ones."