Optimization And Application Of Measurement And Traceability Methods For Black Carbon Aerosol

In this study,we use AE33 Aethalometer（Magee Scientific Inc.）and SUNSET OC/EC analyzer（SUNSET,Inc.）to measure the black carbon of the northern suburb in Nanjing 2020.Then we Compared the two measurement instruments through the method of field measurements of light absorption method measuring parameters are optimized in the process of measurement.Through the improvement for the band transmission measurement of SUNSET,we calculated the BC source parameters again.The use of various methods to source black carbon results in Nanjing,Finally,the time distribution and source of black carbon in the suburbs of the north of Nanjing in 2020 were analyzed.The traceability results of different methods were consistent.The main conclusions are as follows:（1）There was a good correlation between BC and EC,and this relationship optimized the mass absorption cross-section parameters of different seasons.After optimization,the average value of BC was 2.37±1.46μg/m³ and 1.77±1.07μg/m³ during the whole study period.The optimized results decreased by about 25%compared with the actual results,and the trend was consistent with that before optimization.（2）The AAE results of EC in different seasons were obtained by fitting the AAE with the dual-band EC absorbance.The absorption ratio of BC at 370nm was 80%in the whole study stage,and the absorption ratio after adjustment was 61%,which decreased by about 20%.（3）There were noticeable seasonal changes in BC in 2020,and the overall trend was winter>autumn>summer>spring.The diurnal variation of BC is unimodal,and the maximum value appears at 7 am.The meteorological condition that affects BC is atmospheric boundary layer height.When the atmospheric boundary layer height increased,the content of BC decreases significantly.There is a significant negative correlation between BC and atmospheric boundary layer height.,but this relationship has substantial seasonal differences,and the correlation is shown as spring>autumn>summer>winter.（4）BC and NO_x showed a good correlation in the whole season,while BC and SO₂ only showed a specific correlation in winter.It is proved that there is a significant relationship between BC emissions and coal combustion in winter and between BC emissions and motor vehicle emissions throughout the year.BC/PM_2.5 fluctuates around 0.1 throughout the year and decreases significantly in the biomass burning season（autumn and winter）,while it increases considerably in the non-biomass burning season（summer）.BC/CO varies little throughout the year,less than 0.0052.Black carbon absorption accounts for about 80%of the overall absorption,with primary brown carbon accounting for 13%and secondary brown carbon accounting for about 7%.Secondary brown carbon>in spring and summer,autumn and winter,and reaches its peak in spring.The content of BC_bb and BC_ff was 0.31±0.28μg/m³ and1.39±0.83μg/m³ in the whole period.Several methods showed that the main source of black carbon aerosol in Nanjing was motor vehicles.The monthly and seasonal variations also reflected the significant decrease in Nanjing biomass combustion sources in summer and motor vehicle sources during the city closure period.