| Mineral dust is an important component of atmospheric aerosols.The direct radiative effect(DRE)of mine dust aerosol can lead to direct climate feedback effect,which plays an important role in climate and environment change at regional and global scales.Mineral dust(MD),black carbon(BC),and brown carbon(BrC)together constitute the absorbing aerosols(LAAs)in the atmosphere,especially in the North China,where air pollution is severe and obviously affected by dust sources.However,the current understanding of the light-absorbing characteristics and contributions of MD in the atmosphere is still limited,which affects the accurate and comprehensive evaluation of the radiation effect of the LAAs.This study combines multi-site online monitoring data with offline sample analysis data during the dust period to analyze the impacts and corresponding contribution of MD fractions to the quantitative characterization of mass concentration,light absorption properties and relative radiative forcing of LAAs during the dust period.In this study,six urban stations(Wuhai,Shijiazhuang,Dezhou,Jinan,Qingdao and Nanjing)were selected as online monitoring stations along the dust transport path during the strong dust event in northern China in the spring of 2021.The simultaneous observations of newly developed multi-wavelength aethalometers(AE-33)and heavy metal analyzers were used to quantify the mass concentrations of MD,BC and non-BC light absorbers(Delta-C),and to discuss the differences in the concentrations of various types of light-absorbing aerosols and their diurnal variation during dust and non-dust events;the traditional "two components" Aethalometer model was improved,and the absorption coefficients,absorption contributions and diurnal variations of MD,BC and BrC were resolved to compare the differences in the absorption properties of various types of light-absorbing aerosols during dust and non-dust events;finally,the relative radiative forcing between MD,BC and BrC was evaluated by a simplified model.Total suspended particle(TSP)samples were collected from the Qingdao site as an offline monitoring site,and carbonate was removed from the TSP samples by acid fumigation.The elemental carbon/organic carbon in the samples before and after the acid treatment was analysed by the thermal-optical method.The effect of the presence of the carbonate fraction in the mineral dust on the quantitative analysis and quantitative characterization of the absorbance properties of the elemental carbon was investigated.The results showed that the mass concentrations of all kinds of LAAs were ranked from high to low as MD>BC>Delta-C.Fossil fuel sources were the main sources of BC at all observation sites,with an average contribution of more than 70%at each site during the observation period.The mass concentrations of MD and Delta-C increased significantly at all sites during the dust period,especially at Wuhai site,which is the nearest site to the sand source.The strong positive correlation between MD,the light-absorbing iron oxides and Delta-C indicated that the light-absorbing iron oxides in the MD were important contributors to the Delta-C.The light absorption of MD decreased with the increase of wavelength.During the dust period,the absorption coefficient of MD increased significantly at all sites,especially near the sand source sites and the short-wavelength range.The contribution of MD to the total LA As at 370 nm could reach up to 25%at Wuhai site during the dust period.Compared to the non-dust period,the direct absorption of solar radiation by MD increased by 7.6%-46.8%and 3.9%-24.2%at 370-470 nm and 370-950 nm,respectively during the dust periods.The OC/EC analysis results of acidified samples directly confirmed the influence of the presence of carbonate,one of the important components of MD,in the particulate matter samples during the dust period.This study found that the presence of carbonate can lead to overestimation of EC and OC mass concentrations based on traditional thermo-optical analysis,underestimation of the total absorption coefficients of aerosols(especially at long wavelengths),and underestimation of the light absorption coefficients of EC(especially under the influence of strong dust).This was mainly due to underestimation of the mass absorption cross section of EC.Overall,the results of this study provide basic data,such as the concentration levels,light absorption coefficients,and light absorption contributions of three typical LAAs(e.g.,MD,BC,BrC)at different urban sites in northern China during dust events,as well as the mass absorption cross section of EC.It is helpful to comprehensively understand the concentration level,light absorption contribution and relative radiative forcing of mineral dust aerosols in the future.Furthermore,it also provides reference and basic data for subsequent evaluation of radiation effects of various LAAs. |
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