Zhu Yuzu, manager of a privately owned brick factory in northwest China's Gansu Province, will have a long winter vacation starting on Thursday.

His factory, in the capital city of Lanzhou, Gaolan Yellow River Brick, will suspend production till the end of March 2011.

Zhu's factory is among the 77 brick and tile manufacturers in Lanzhou that were ordered to halt production in a government move aimed at improving the city's air quality.

Previously, the government had ordered closure or limited production from 65 local manufacturers, including 28 brick and tile producers, during the winter season.

These factories are partly blamed for the grimy air that engulfs the inland city in winter when air pollution reaches its worst.

"The factories were shut down mainly because they heavily pollute and their emissions are not up to the standard required," said Kang Mingke, director with the legal department of the Lanzhou Environmental Protection Bureau.

Most of these factories are small, private businesses that are unable to afford expensive emission control systems, Kang said.

The Lanzhou government has, in recent years, ushered in a package of measures, including shutting down heavily polluting industrial projects and controlling car emissions, in an effort to improve the city's air quality.

So serious was the air pollution in Lanzhou in the winter of 2007 that then-Mayor Zhang Jinliang encouraged civil servants to give up driving and walk to work.

"The air is so thick in the winter that the whole city is just like a coal-burning stove," said Wang Chenghu, a local resident who has lived in the city for over a decade.

Wang told reporters that because of the pollution, he had sent his one-year-old grandson back to his hometown in the eastern Anhui Province.

"It is hard for adults to endure, let alone young kids," Wang complained.

Lanzhou has some of the worst air pollution in China. According to data released by the Ministry of Environmental Protection, Lanzhou topped the list for air pollution among 86 cities across the country that were monitored this past Monday and Tuesday.

Located in a narrow river valley with surrounding mountains blocking a free flow of air, the city suffers in the winter from large dust storms kicked up from the desert to the north.

Moreover, the municipal heating system that relies heavily on coal burning, aggravated air pollution in the winter. [ Though industrial enterprises contribute much to the city's economic growth, they are also the main sources of air pollutants as coal is widely used for production, said Yao Guoqing, vice mayor of Lanzhou.

"We shall focus on harnessing the sources of industrial pollution in dealing with winter air pollution," said Yao, noting that production of heavily polluting factories should be limited, suspended or closed down.

The city, however, is facing a dilemma. As one of the least developed capital cities in China, Lanzhou has to continue developing economically, even while closing local industries.

"There is a strong appeal for the improvement of air quality among our citizens, and it is an absolute responsibility for our government to curb polluting sources," said Mayor Yuan Zhanting.

The Lanzhou government has invested more than 4 billion yuan (600 million U.S. dollars) during the past five years for environmental improvement.

"The decision to halt production of brick and tile factories is made upon consideration of actual conditions," said Kang, noting that production in winter is slowed down because of low temperatures, which will also increase energy consumption and emissions.

Surprisingly, the decision was supported by many of the brick and tile factories.

"Lanzhou has special geographical and climatic conditions that have an impact on the air pollution. The decision to suspend the production is justifiable," said Xiao Zhenbang, manager of a local brick factory.

"The administration of environmental protection issued the notice in advance, and we have arranged the production correspondingly. We were well prepared for it," Xiao said.

Employees of these factories are mostly migrant workers who are flexible in finding new jobs. Further, some factories will offer migrant workers subsidies or prepaid salaries to build a working force when production resumes in April next year.