Aerosol Optical Properties On Haze Pollution Days And Remote Sensing Detection Of Aerosol Inter-provincial Transmission

Aerosol haze pollution days(HPDs)occur frequently in eastern China and make a profound impact on regional air quality and global climate.A statistical analysis of aerosol optical properties and direct radiative forcing on the HPDs from 2013 to 2016 at two AERONET sites(Beijing-RADI and Xuzhou-CUMT),were conducted by using Sun-sky radiometer measurements.The results show that: 1)The total HPDs numbers during 2013–2016 in Beijing and Xuzhou were 377 and 292,respectively.There were from 40% to 50% effective data of AERONET data for HPDs and more than half for non-haze pollution days(NHPDs).2)There were very high proportions in winter at both sites,more than half at Xuzhou and one-third at Beijing,respectively.3)Average values of aerosol optical depth at 500 nm(AOD500nm)on the HPDs were about 3.7 and 1.6 times greater than those on the NHPDs in Beijing and Xuzhou,respectively;on the NHPDs,Xuzhou had near two times larger AOD than Beijing showing a higher background level of aerosol loading.4)For Angstrom Exponent(?)<1.0 and ? >1.0,the relative frequencies of ? at Beijing were 26.05% and 73.95%,respectively;while those at Xuzhou were 5.81% and 94.19%,respectively.It suggested that HPDs in Beijing were more susceptible to coarse dust particles than in Xuzhou.The averaged values of fine-mode fraction(FMF)on the HPDs were 0.778 and 0.882 in Beijing and Xuzhou,respectively.It indicated that the haze pollution was dominated by fine particles.5)The highest volume size distribution and radius in the fine mode occurred in summer,due to aerosol hygroscopic growth.From the analysis of SSA and complex refractive index,we can see that aerosols over Beijing showed stronger absorption ability,while showing stronger scattering over Xuzhou.6)On the HPDs,giving rise to averaged atmospheric direct aerosol radiative forcing(DARF-ATM)were 77.472±49.665 W/m2 in Beijing and 42.573±28.819 W/m2 in Xuzhou,respectively.The larger values of DARF-ATM observed on the HPDs showed a heating effect to the atmosphere,and a low AOD could present more impact on aerosol radiative forcing efficiency.These results will help to assess haze radiative forcing effects in China,and to improve satellite aerosol retrievals under haze conditions.From December 2014 to January 2015,the ground-based Lidar(Mini MPL)in Xuzhou were used to detect the aloft-haze-plume events.The HYSPLIT backward trajectory model was used to understand the inter-provincial transmission process,and the variation of optical characteristics was investigated with and withnot haze plume intrusion into the PBL(planetary boundary layer)from the free troposphere.The results showed that in all aloft-haze-plume events,haze plume was mixed into the PBL from the free troposphere.As the intrusion of aerosol,the optical thickness of the PBL gradually increased.When there is aloft-haze-plume,AOD500 nm,?,and FMF became larger,suggesting that high aerosol loading and more fine particles.