Environment authorities in Beijing will no longer use the method of counting "blue sky days" as a gauge of air quality, which had been practiced for more than a decade.

Beijing has used a five-grade classification of air quality on the basis of pollution indices, with grade I being the best and grade V the worst. Days with grade I or II air quality are considered "blue sky days."

The city launched the "Defending the Blue Sky" project in 1998, when it had only 100 days of "blue skies."

"But 'blue sky days' are only an average figure and can hardly reflect the specific situation of different areas in the city due to various factors including climate, geography and emission," said Yu Jianhua, director of the Air Quality Department under the Beijing Municipal Environment Protection Bureau, on Tuesday.

"Therefore, the air quality results we released were always different from the true feelings of the general public," he said.

Yu said local environment authorities will no longer count "blue sky days" starting this year.

"We will release the concentration indices of major pollutants for different areas in Beijing to measure the air quality, including particulate matter, sulfur dioxide and nitrogen dioxide," he said.

The municipal government has set pollution-reduction targets for different districts and county governments in the city for 2012, which require an average 2 percent decrease of concentration indices of major pollutants compared with those last year, he said.

In 2011, Beijing enjoyed 286 days of "blue skies," or 78.4 percent of the year, according to an environment report issued Monday, a day ahead of the World Environment Day.

"That was our last report on 'blue sky days'," Yu said.

China currently uses PM10, or particular matter under 10 micrometers, to measure air quality, but the public has urged government authorities to apply the stricter PM2.5 standard, which measures finer matter that is considered more hazardous to people's health as it can go deeper into the lungs.

The Ministry of Environmental Protection has ordered 74 cities to apply a more comprehensive air quality monitoring standard and publish daily reports on PM2.5 by the end of this year.

Cities in the Beijing-Tianjin-Hebei region, Yangtze River Delta and Pearl River Delta, as well as southwest China's Chongqing municipality and all provincial capitals, have been asked to monitor for PM2.5 starting in October and publish monitoring results before the year's end, the ministry has announced.

Beijing began to release hourly PM2.5 readings in January, but only covers a few areas in the city.

"We are purchasing more equipment for monitoring PM2.5," Yu said.

"By the end of this year, all 35 monitoring stations will be built around the city and began releasing data in this regard," he added.