Relationship Between Haze Pollution And Aerosol Properties In The Yangtze River Delta Of China

City clusters in eastern China have endured heavy haze pollution in recent years.Scientific questions about the relationship between visibility and aerosol properties havebeen raised. Focusing on the Yangtze River Delta (YRD), this study investigated thelong-term trend of haze pollution, typical haze pollution types and their formationmechanism, and the relationship between the extinction coefficient and particulatematter pollution through the investigation of historical data, regional field observationand enhanced observation experiments. The results of this study will provide strongscientific support for the assessment and control of haze pollution in China.The analysis of visibility, meteorological and pollution change in the past thirtyyears indicates that the visibility has decreased from15.7km in1980to13.2km in2010in the YRD region. For Hangzhou, Nanjing and Suzhou, the numbers of haze dayshave increased from50,40and20in1980to160,140and70after2001. The increaseof particulate matter concentrations, especially the fine particulate matter (PM2.5) is thereason for visibility degradation.Based on the results of one-year regional observation for five cities at six sites,four typical haze types are identified: dust storms in spring with the dominantcomponents being crustal elements in coarse particles; biomass burning in the summerproducing a contribution of23-48%of PM2.5concentration; PM2.5pollution in autumnaffected by both the temperature inversion, biomass burning and heavy fog events; andwinter pollution impacted by the stable meteorological conditions after cold fronts aswell as the trans-provincial transport of air pollution in the YRD area.The mass extinction efficiencies of PM10, PM2.5and PM10-2.5are estimated to be2.25,4.08and0.58m2/g, respectively. The contribution of PM2.5and PM10-2.5toextinction is40%and4%, while the hygroscopic growth contributes56%. Based on themass extinction efficiency of particulate matter, the thresholds of particulate mattermass concentration for the cases of visibility lower than10km are estimated. Thethresholds for PM10are133μg/m3under any relative humidity (RH) and67μg/m3under the annual average RH. The corresponding thresholds for PM2.5are73and38μg/m3, respectively. It is found that the original version of the IMPROVE algorithm underestimates by31%of the light extinction and the revised version overestimates by10%, comparedwith the measurement data. The mass scattering efficiencies calculated from theobservation data in the YRD are3.46m2/g (3.40during clean episode and4.12duringpolluted episode) for ammonium sulfate,4.02m2/g (3.93for clean episode and5.10forpolluted episode) for ammonium nitrate, and4.49m2/g for organics (4.40for cleanepisode and5.53for polluted episode), respectively. The hygroscopic growthcontributes31-38%to the annual average extinction, followed by organic compoundswith a contribution of19-23%, while the contributions of ammonium sulfate,ammonium nitrate and black carbon vary in the range of10-18%.