Beijing's government on Friday bowed to a vocal online campaign for a change in the way air quality is measured in the Chinese capital, one of the world's most polluted cities.

Authorities said they would start publishing figures this month showing the smallest, most dangerous pollution particles in the air after considering the wishes of residents, expressed on China's popular microblogs.

The Chinese capital currently bases its air quality information on particles of 10 micrometers or larger, known as PM10, and does not take into account the smaller particulates that experts say are most harmful to human health.

But authorities came under huge pressure to change the system last year when they ranked the air as only slightly polluted, despite thick smog that forced the cancellation of hundreds of flights and triggered a surge in face mask sales.

The local government already measures particles of 2.5 micrometers or less, known as PM2.5, but China's environment ministry had said the data would not be available nationwide until 2016.

On Friday the Beijing Environmental Bureau said it would provide hourly updates of PM2.5 measure ahead of the Lunar New Year, or Spring Festival, which starts on January 23, in response to the flood of public anger.

"The authorities plan to release air-quality monitoring data using PM2.5 before Spring Festival," a bureau official surnamed Jiang told AFP.

"The government has to consider the pleas of the people, so yes, the anger of Beijing citizens these days is a big contributor to our action."

Public anger was exacerbated by the discrepancy between the official data and that issued online and on Twitter by the US embassy in Beijing, which conducts its own measures of PM2.5 and frequently registers dangerous pollution levels.

Many bloggers hailed the role of the US embassy in the Beijing government's apparent change of heart. "The effort of the US embassy should not be ignored," posted one under the name Kangtou Wang on Sina weibo -- China's biggest microblog.

China has the world's largest online population, with around half a billion web users, posing a growing challenge to authorities in a country that tightly controls its media.

Although censored, the microblogs are proving to be a highly effective public platform for people to call officials to account and report government or corporate malpractice and other problems.

The public response to the announcement was mixed, with some residents welcoming the move, while others expressed suspicion about the government's true intentions.

"The trend nowadays is to clean up problems only when they show," posted one user under the name Qiong Xiaobing on Sina's weibo.

"We don't care about data or figures, there's nothing we can do about pollution even it exceeds the limit," wrote another Sina weibo user under the name Hebo HB.

"We have already been living like this for decades, we only wish the government would not cheat us."

Beijing authorities said last month they had met their target of "blue sky" days for 2011, with 274 days of "grade one or two" air quality compared with 252 days in 2010.

But the state-run China Daily has said that if PM2.5 were used as China's main standard, only 20 percent of Chinese cities would be rated as having satisfactory air quality, against the current 80 percent.

International organisations including the United Nations list Beijing as one of the most polluted cities in the world, mainly due to its growing energy consumption, much of which is still fuelled by coal.

A doubling of coal consumption over the last decade and booming auto sales that have made China the world's biggest car market have negated the impact of pollution control efforts in recent years.

Chinese environmental groups welcomed the latest move, saying it would result in a better understanding of the dangers of pollution.

But Wang Qiuxia, an air pollution expert with Chinese group GreenBeagle, warned that cleaning up Beijing's air would be a long process.

"According to some assessments it will take 20 years before we see an improvement in Beijing's air quality, provided that proper measures are adopted," she said.