Recently,ash haze pollution became the main problem of atmospheric environment in China.As one of the important precursors [1] of secondary organic aerosols (SOA) of heavy haze pollution,NOx is typically characterized for low concentration (ppb) and difficult to remove,therefore research on air purifying technology of high efficiency is very important.Compared with traditional methods (such as physical adsorption and biological filtration),semiconductor photocatalytic technology has the advantages of high efficiency,low cost and energy consumption,which is widely used in air pollution control.