Heavy fog and pollution have enveloped several northern and eastern Chinese regions including Beijing for almost two weeks now. Motorways have been closed and hundreds of flights delayed or even cancelled.

Heavy fog and pollution have enveloped several northern and eastern Chinese regions including Beijing for almost two weeks now.

The public has been calling for the Beijing government to better monitor air quality in the city, and inform residents of the state of air pollution.

Beijing was encased in its thickest hazes last month.

The city’s environmental watchdog attributed the situation mostly to the weather.

Du Shaozhong, spokesman of Beijing Environmental Protection Bureau, said, "In Beijing, the haze occurs every time the season changes. When fog continues for several days, it could happen. I've been living in Beijing for over fifty years. From my personal experience, it's normal. It's not pollution."

He says that's exactly what happened in October. The thick fog shrouding Beijing and most parts of North China lasted for several days, resulting in a sharp drop in air quality.

"I don't agree with the accusation that the air quality of Beijing has been worsening or made no progress over the past few years. What we experienced last month could have been a lot worse if it happened five or six years ago," said Du.

The disparity in the air quality monitoring results released by Beijing's weather forecast station and the US Embassy in Beijing provoked mass debates.

These differences are because of the different standards of measurements used.

The US embassy gauges air pollution with the PM 2.5 or Particulate Matter 2.5, which charts dust particles with diameters no larger than 2.5 micrometer. Chinese regulations on the other hand, measure with the PM10, which chart larger, but less-harmful to health dust particles.

Du said, "We are making detailed standards to better monitor air quality, following the requirements of the Ministry of Environmental Protection."

Both the US embassy and the Beijing Environmental Protection Bureau have agreed their figures should not be compared with each other. According to Du Shaozhong, the bureau's result marks the average level of 27 monitoring stations.