TAIYUAN - Ma Liang was trawling the Internet looking for a bag filter that could be used at the steel plant he works at.

Amid public calls for cleaner air, the Taiyuan Iron and Steel Group Co Ltd in northern China's Shanxi province, which burns coal and coke for energy, is stepping up efforts to reduce particulate discharge.

"I am looking for a filter made of thinner fiber that can reduce particulate emission by half," said Ma, who is head of the pollution control division of the firm.

The company is not alone.

Coal-burning factories, like steel plants, thermal power companies and central heating providers are looking to use bag filters to reduce dust, at a time when air quality has become a big complaint among Chinese citizens.

The bag filters, which come in different sizes and can used in apartments or big factories, allows air to go through it and is cleaned as the filter catches dust.

When carrying out market research, Ma found bag filters, made of a new kind of material, which sell roughly the same as the old ones. "The material also allows better air permeability, so we do not have to change fans," Ma said.

"So the overall cost will not increase," he said, adding that price is an important factor when it comes to environmental protection as the Chinese steel industry is generally suffering from over-supply and weak demand.

Air quality is a big challenge in China. Heavy smog affected 800 million people at the beginning of the year. In summer, humid weather makes dust and smoke in the air difficult to disperse.

Automobile exhausts, industrial emissions, coal-fired heating, as well as dust from construction sites are to blame for the country's smog, according to a number of experts, including Wang Yuesi, a researcher with the Chinese Academy of Sciences.

Drivers have been discouraged in using automobiles but it is difficult as many do not want to sacrifice convenience and the air quality will not be improved if just a few Chinese people do so.

Dust from construction sites will not decrease either given that the country is at a stage of fast urbanization, accompanied by building new apartment blocks, subways and other large projects.

China is making more efforts in cutting emission from factories through launching tougher industrial standards throughout the year. Plants now use both bag filters and electrostatic precipitators to reduce particulate discharge. Bag filters are encouraged in the new standards for better performance.

Industry figures showed that 90 percent of thermal power units with generating capacity of 800 million kw or higher in China are installed with electrostatic precipitators, according to a report of Minsheng Securities.

If all these units were added with bag filters, it would cost about 50 yuan ($8.15) for upgrading each kilowatt of generating capacity. That translates into a potential market of 36 billion yuan, said the report.

Located within the city of Taiyuan and close to densely-populated areas, Taiyuan Iron and Steel Group is taking the lead in using bag filters to reduce dust.

Ma said once the new bag filters are in place, the company will cut particulate emission from 20 mg for every cubic meter to 10 mg.

More companies in the country are installing bag filters.

In Xilian Heating Company in northwest China's Xi'an, iron boxes with bag filters inside are installed on coal-fired boilers.

The old filtering facility on the boiler can reduce particulate emission to 80 mg for every cubic meter. With the new box, emission can be cut down to 30 mg, according to the company.

The Xi'an Environmental Protection Bureau is encouraging technological upgrade at local heating companies and expects more bag filters to be installed before winter.