CHECKING THE AIR: A worker at the Beijing Environmental Monitoring Center adjusts the monitoring equipment for the PM2.5 measure of air quality in Beijing on January 7 (GONG LEI)

Starting on February 2, a new figure showing the 24-hour average concentrations of PM2.5, an important gauge of air quality, appeared on the website of the Beijing Municipal Environmental Protection Bureau (EPB).

Earlier, the bureau started to publish hourly readings of PM2.5 on January 21.

PM2.5 refers to fine particles 2.5 microns or less in diameter, which are believed to pose greater health risks than larger particles because they can penetrate people's lungs or even enter the blood stream.

"The hourly data reveals the instant increase in PM2.5 density, but fails to indicate the overall air quality of the day," said Zhao Yue, Deputy Director of the Beijing Environmental Monitoring Center (BEMC).

By comparison, the 24-hour average data is a standard adopted by many developed countries. "It precisely shows the overall air quality and makes it much easier for the public to judge whether the air is harmful to their health or not," Zhao said.

Besides the new daily average, BEMC is also ready to release hourly measurements of three other types of airborne matter—sulfur dioxide, nitrogen dioxide and inhalable particles.

Public promotion

Beijing residents have long been dissatisfied with the official air quality figures, saying they fail to reflect the real level of danger to inhabitants. They called on the government to adopt the tighter PM2.5 standard, instead of the previous PM10, or fine particles under 10 microns in size, to measure air quality.

Wang Yuesi, a researcher at the Institute of Atmospheric Physics of the Chinese Academy of Sciences, has been monitoring data of both PM2.5 and PM10 since 1998. His studies found that the average density of PM10 in Beijing is decreasing at a rate of 2-3 percent every year, but PM2.5 concentrations are increasing by 3-4 percent on an annual basis.

Wang said that the growing number of motor vehicles and increasing industrial pollution contribute to a higher concentration of smaller particles.

According to official data, the average annual PM2.5 density in Beijing was 70-80 micrograms per cubic meter in 2010, more than double the target of 35 micrograms a cubic meter set by the Ministry of Environmental Protection (MEP).

Scientists estimate that 50 percent of the total PM2.5 particles in the air are contributed by automobile exhaust, and another 23 percent are brought by floating dust.

Beijing is not the only city facing a public outcry over pollution. Many Chinese cities are periodically enveloped in heavy smog, deepening public frustration over the quality of the air people breathe every day.

According to the Shanghai Environmental Monitoring Center, the average annual density of PM2.5 in the city was 44-53 micrograms a cubic meter in 2006-10.

"A pilot monitoring program for PM2.5 in nine cities, including Shanghai, Tianjin and Guangzhou, since 2007 shows that particulate pollution is a common challenge," said Luo Yi, Director of the China National Environmental Monitoring Center.

"Including PM2.5 readings is an essential part of tackling the country's haze problems, and it reflects the growing influence of public concern on air quality monitoring," said Ma Jun, Director of the Beijing- based Institute of Public and Environmental Affairs.

On December 21, 2011, after more than one month of public hearings, the MEP laid out a detailed timetable for Chinese cities to monitor PM2.5.

According to the timetable, cities in the Beijing-Tianjin-Hebei region, the Yangtze River Delta and the Pearl River Delta, as well as southwest China's Chongqing Municipality and provincial capitals, should start monitoring PM2.5 and ozone in 2012.

The new air quality standards will apply to the whole country by January 1, 2016, and the monitoring results will be made public.