A field campaign on air quality was carried out in Shanghai in winter of 2012.The concentrations of NO,NO2,NOx,SO2,CO,and PM2.5 increased during haze formation.The average masses of SO42-,NO3-and NH4+ were 10.3,11.7 and 6.7 μg/m3 during the haze episodes,which exceeded the average (9.2,7.9,and 3.4 μg/m3) of these components in the non-haze days.The mean values for the aerosol scattering coefficient (bsp),aerosol absorption coefficient (bap) and single scattering albedo (SSA) were 288.7,27.7 and 0.91 Mm-1,respectively.A bi-peak distribution was observed for the mass concentrations of CO,NO,NO2,and NOx.More sulfate was produced during daytime than that in the evening due to photochemical reactions.The mass concentration of NH4+ achieved a small peak at noontime.NO3-showed lower concentrations in the aftoon and higher concentrations in the early ming.There were obvious bi-peak dial patts for bsp and bap as well as SSA.bsp and bap showed a positive correlation with PM2.5 mass concentration.(NH4)2SO4,NH4NO3,organic mass,elemental carbon and coarse mass accounted for 21.7％,19.3％,31.0％,9.3％ and 12.3％ of the total extinction coefficient during non-haze days,and 25.6％,24.3％,30.1％,8.1％ and 8.2％ during hazy days.Organic matter was the largest contributor to light extinction.The contribution proportions of ammonium sulfate and ammonium nitrate to light extinction were significantly higher during the hazy time than during the non-haze days.