Chemical And Light Absorption Characteristics Of Particulate Matters And Their Source Apportionment Over Qingdao And South Yellow Sea

PM2.5(particulate matter with an aerodynamic diameter of?2.5 ?m)is a crucial air pollutant,emitted from the both natural and anthropogenic sources resulting to a complex composition containing water-soluble inorganic species(ionic species),organics(including organic carbon:OC and elemental carbon:EC)as well as trace metals.Black carbon(BC)is the product of emissions from the incomplete combustion of fossil fuels or biomass.It is also considered to be primary absorbing particulates resulting in the second-highest climate warming pollutant after CO2.Black carbon mass absorption cross-section(MAC)is an important parameter to describe the optical properties of black carbon,and influenced by several factors such as black carbon emission sources,chemical composition,aerosol aging and mixed morphology.Due to the aging of aerosols,freshly emitted black carbon is mixed with non-absorbent substances.The coating will increase the mass absorption cross section(MAC)of black carbon which causing the absorption enhancement effect of black carbon.It is characterized by black carbon enhancement of MAC(EMAC).Due to the lack of significant measurement of MAC values at different wavelengths,a large uncertainty in global direct forcing is still observed.Therefore,it is urgent to establish an effective observation method to directly measure the light absorption enhancement effect of black carbon in the atmospheric environment.In addition,the emission source contribution to EMAC still remain highly unclear and only a few studies focused on the specific source apportionment of EMAC at present.Therefore,in the present study,we quantified EMAC to indicate the enhanced light absorption intensity of BC under the action of the coating from the different emission sources.In order to investigate the spatial,temporal,chemical characteristics,source apportionment and light absorption characteristics of PM2.5,an intensive simple was conducted simultaneously at North China coastal site(Qingdao city)and maritime sites(the South Yellow Sea,SYS)in August and Nov-Dec 2018.In this study,13 trace elements(Fe,Mn,V,Zn,Be,Co,Cr,Ni,Cu,Rb,Cd and Pb),7 water soluble inorganic ions(Na+,NH4+,K+,Ca2+,Cl-,NO3-and SO42-),organic carbon and elemental carbon was determined.At the same time,the main sources and variation characteristics of PM2.5 are analyzed by positive matrix factorization(PMF)model.On this basis,we remove black carbon coating through the aerosol filter filtration-dissolution(AFD)system,separated black carbon from aerosols and get"pure" black carbon in the atmosphere.By comparing the mass absorption cross section(MAC)of black carbon before and after AFD treatment,Thus,the absorption enhancement factor(EMAC)of secondary aerosol coatings on black carbon was directly observed.Finally,PMF was used to quantitatively evaluate the contribution of various pollution sources to black carbon absorption enhancement for the first time.The results showed that(1)SI A(as the sum of SO42-,NO3-,and NH4+)were constituted the largest fraction accounting for 41-61%.The high NO3-/SO42-ratio indicated mobile sources contributed more than stationary source of PM2.5.The average ratio of OC/EC was ranged from 3.71 to 5.56 indicated there were severe secondary organic pollution.(2)A two-step solvent treatment was employed to remove both organic and inorganic coatings,and the absorption enhancement(EMAC)of the BC is found 1.96±0.68(QS),1.64±0.38(QW),2.40±0.76(SYS),respectively.(3)Positive matrix factorization(PMF)model identified six sources of PM2.5 and EMAC,which were secondary aerosol(with contribution 27.9%and 29.2%),coal combustion(24.9%and 20.2%),industrial emissions(15.2%and 25.4%),sea salt(6.9%and 9.6%),vehicle emissions(12.1%and 10.9%)and soil dust(13.0%and 4.7%),respectively.(4)These sources increased the absorption of black carbon by a factor of 1.25±0.11(secondary aerosol),1.21±0.20(industrial emissions),1.17±0.08(coal combustion),1.09±0.07(vehicle emissions),1.08±0.17(sea salt),and 1.04±0.10(soil dust).(5)Based on the correlation between PM2.5 and EMAC source contributions,we estimated that secondary aerosols,industrial emissions and coal combustion contributed to 74.8%of absorption enhancement at a regional scale in China.The source apportionment for EMAC offers new diagnosis for each source regarding aerosol forcing simulation which inputs from individual emission sector.