Observational Study On Physicochemical Properties Of Black-carbon Aerosols Under Representative Atmospheric Environments

Refractory black carbon(rBC)is an important part of atmospheric PM2.5,a product of incomplete combustion of fossil fuel or biomass/biofuel.rBC is the strongest material that absorbs solar radiation directly,thus plays a significant role in global climate change and visibility impairment etc.By internally or externally mixing with other inorganic and organic components,the mophorolgy of rBC could be completely changed.And thick coat increases the mass absorption cross-section(MAC)of rBC core,enhances its light absorption by"lensing effect".In addition,rBC also can be served as cloud condensation nuclei(CCN)when coated by hydrophilic materials,altering the albedo and precipitation of clouds indirectly.Nevertheless,the emission sources and climate of regions are not the same,which makes a great uncentainty of the composition,mixing state,coating thickness and light aborption property etc.of rBC-containing aerosols.Therefore,directly quantitative measurement of chemical characteristics of ambient rBC-containing particles in different area is thus important to evaluate their climate forcing and control emission sources effectively.In this work,three field studies were deployed in different regions to characterize the ambient rBC-containing aerosols,an Aerodyne soot-particle aerosol spectrometer(SP-AMS)was first applied,combined with a series real-time instruments.First,a specific type of rBC,fullerenes-like carbon cluster(fullc),was confirmed exist in the ambient air ubiquitously.Sources and characteristic method of fullc were discussed.Second,a remote site in Tibetan plateau(TP)and urban Beijing were chosen as the typical clean environment and the typical high-level polluted environment respectively.Ambient rBC-containing aerosols in two representative areas were observed,to investigate the chemical composition,size distribution,mixing state and optical property etc.From 20 Feb to 20 Mar 2015,a field study was conducted at the campus of Nanjing university of information science and technology(NUIST),surrouned by petro-chamical and steel-making industries.During the campaign,fullc was observed strikingly,and the plan was altered to focus on characteristic of fullc.Results shows that the mass loading of fullc was from 0.8 ng m-3 to 83.2 ng m-3,14.0 ng m-3 on average.Multi-linear algorithm was applied on positive metrix factorization(PMF)solutions,indicating that 30%of fullc derived from vehicular emission,with 70%from petro-chemical industy during the sampling period.For rBC,55%was emitted from traffic,45%from petro-chemical industy.Those findings suffiently suggesting that fullc might be sevrve as a tracer of petro-chemical industy or diesel engine vehicles.In addition,this study provides a brand-new method for detecting fullc.From 31 May to 30 June of 2015,observation of atmospheric rBC and associated coatings was conducted at the NamCo comprehensive station of Chinese Academy of Sciece(CAS),as a typical clean environment.Results shows that organic aerosols(OA)coated on rBC in this area mainly much thicker(mass ratio of coatings to rBC core(RBC)was up to 14)than those in urban or rural sites,O/C is 0.51 calculated by Aiken's method on average.Size distribution of chemical-resolved rBC-containing particles mainly uniform,peaking at?500 nm,indicating those particles are internally mixed.It should be point out that biomass burning OA(BBOA)was found usually thickly coated on rBC,contributed more than 30%before monsoon.Through "lensing effect",BBOA plays a significant role in the light absorption ability of rBC,the light absorption enhancement effect(Eabs)eventally can increase by a factor of 1.4.Besides,local souces such as Yak dung burning or combustion of other fuels also exerts an important role in monsoon period,local OA on rBC was over 43%on average.Field study on typical high-polluted urban atmospheric rBC-containing aerosols was conducted during 15 Nov to 13 Dec of 2016.Results shows that mass concentration of rBC both affected by transportation and local emission sources.High-level polluted epsiods usually occurred when the wind dominanted by south direction or the wind speed is very low.PMF results show that photochemical process plays a dominating role in the formation of secondary OA(SOA)coated on rBC,while primary OA(POA)takes over 61%of total OA on average.Comparison of SP-AMS and HR-AMS results show that the temporal variation of OA correlated well in most of time,with quite big difference during some heavy-polluted episodes.Mass loading derived from PAX measured light absorption of rBC at 880nm was used to investigate the light absorption enhancement(Eabs),and the Eabs was up to 1.3.The results of this work show that:(1)fullerenes-like carbon clusters is existing in the atmosphere,and the SP-AMS could be used as a powerful detective method;(2)rBC particles in the clean environment were higher processed than those in the high-polluted environment,and the rBC particles on TP might be presented a core-shell structure,but not in Beijing;(3)The influence of BBOA shouldn't be ignored in the clean area,fossil combustion was the dominated source in urban Beijing during winter,and Cooking-related OA usually does not co-emitted with rBC;(4)Photo-chemical process is the major path of SOA formation.