It has been common knowledge that smoking andrnlong-term exposure to smokers lead to increase risk of lung cancer.rnNevertheless, in has been found in a number of mega cities in China, whilst thernnumber of smokers drops, and the chances of exposure to smokers decrease due to stricter smoking limitation inrnpublic places, a rising trend in obtaining lung cancer in population is stillrnobserved. Therefore, scientists in China started to suspect arnconnection between particulate matters and increased causing of lung cancer.rnUnlike some other air pollutants that consist of just one chemical composition,rnPM2.5 consists of a number of chemical compounds including SOx,rnNOx, NH3, organic chemicals, volatile metals, soilrnand dust particles, and allergens. These compounds are formed in primary and secondaryrnprocesses. Primary particles are generated by combustion, industrial processrnand natural erosion, and secondary particles are generated during processesrnlike nucleation, condensation or particle formation and growth. In China, up tornnow, the research data is very limited about the effect of PM2.5 onrnlung cancer incidence rate, mainly because the concern of PM2.5 onrnpublic health only became a focus after 2008.