The US embassy in Beijing has set up its own air monitoring station out of concern for the health of its staff.
The embassy has been releasing its own private air quality reports since last year, which differ significantly from the ones issued by the Beijing government, spokesperson Susan Stevenson said in an interview last week with Canwest News Service.
People can check the air quality near the embassy on a Twitter feed called BeijingAir, with the latest information updated every hour.
From 1 am to 2 pm yesterday, the air quality was "unhealthy," according to the embassy monitoring station, while the capital's environment protection bureau said that the average air quality yesterday in Chaoyang district, where the embassy is located, was "moderate".
The air quality for June 18, when the sky was murky at noon, was "slightly polluted," according to the official data, but the result was different on the BeijingAir Twitter, with the hourly measure creeping into the "hazardous" range for seven hours.
China Daily calculated that only five days were above "moderate" level in May on BeijingAir, but the local environment bureau said on its website on May 31 that the capital's air quality was the clearest during the same period since 2000, with 25 blue-sky days.
"This is a single site," Stevenson said. "It cannot be used to measure the air quality across the city. They can't be compared."
A blue-sky day is when the city's air pollution index, the level of five airborne pollutants, falls below 100, indicating that no health implications exist.
Because environmental standards are not uniform and monitoring stations throughout Beijing can record different data, air pollution readings vary, environment officials and experts said yesterday.
Li Xin, chief engineer of the municipal environment protection bureau, said yesterday that the bureau has 27 monitoring stations across the city and publishes average air quality data every day.
"The embassy is located in the central business district, which has heavy traffic, and its monitoring station cannot represent the overall picture," Zhu Tong, an environment professor with Peking University, said yesterday.
The different measuring standards also matter.
US environmental protection agency standards measure particles less than 2.5 micrometers in diameter (PM 2.5) that go into people's lungs and bloodstream when breathing while China measures particles less than 10 (PM 10).
Zhang Jianyu, China program head of the US-based Environmental Defense Fund, said PM 2.5s will be part of the air quality evaluation system to offer people a clearer picture of air quality. The bigger particles are seen as less dangerous, he said, because they can usually be expelled from the body by coughing.
The current evaluation system uses only three indices: Sulfur dioxide, carbon dioxide and PM 10s.
Some residents expressed doubts about the official air quality data.
Wang Haiyan, a 36-year-old Beijinger living in Chaoyang district, said that even under a different measuring system, there is still no reason to get such different air quality results.