what kind of factory u talking about? There are factories that make toys factories that make cars, factories that make phones and some make shoes. I think the pollution comes from the cars not the factories..you are welcome!

From the article: Beijing's Air Pollution: It Isn't the Cars, dated around Olympics time 

"The real causes of Beijing’s air quality woes lie elsewhere. An article last year suggested the key component to Beijing’s ozone problem (the stuff that makes your eyes itch, causes shortness of breath and reduces visibility) is actually volatile organic compounds (VOCs) from small factories in neighboring Hebei province. A sniff test suggests that there are plenty of these factories operating in and around Beijing. Many are small (and possibly illegal), and they operate only at night to avoid the scrutiny of environmental inspectors. So the Beijing government has several problems: first, it must locate these hidden factories. Then they must shut them down—and convince neighboring provinces to do the same.

Beijing’s other major problem is particulates, which come from several sources. One is construction: Beijing is still rushing to complete non-Olympic buildings before the big day. Another is coal-fired power plants and factory boilers. China’s largest coal-mining province, Shanxi, is directly up wind of Beijing. Shanxi ships much coal to other provinces, but it also has mine-mouth power plants and coking plants that contribute to regional pollution.

A final source is trucks. As with the VOCs from small factories, emissions from heavy vehicles are worst during the night, since trucks are banned from the city during the day. Studies have shown that Beijing’s pollution levels are highest in the early morning. This would not be the case if most of the pollution came from passenger cars, which operate mainly during the day. But it is good evidence that the chief sources of pollution are the VOC-producing factories and trucks operating at night.

The international focus on Beijing’s car problem, when the true problem lies more with industrial emissions, suggests we often apply lessons from one place a little too readily to another. China’s air pollution problem—like its [greenhouse gas emissions](node/9331)—is primarily connected to industry. There is no question that smart transportation planning would help China avoid vehicle-caused smog and global warming in the future. But for the here and now, the real challenges are in industry, and the real efforts need to be in strengthening local enforcement of existing pollution and energy efficiency standards and with developing new multipollutant standards that address issues like VOCs."