Spatial Distribution And Sources Analysis Of Black Carbon Contents In Snow Of Typical Snow Area Across Northern China

Black Carbon is the strongest light-absorbing component in snow cover.It can reduce the surface albedo,accelerate the melt of snow and ice,and consequently changes the characteristics of surface runoff and internal water circulation,which plays an important role in global climate change.The field campaign had been carried out across northern Xinjiang and the Tianshan Mountains region,the Northeast region and the central and eastern Qinghai-Tibet Plateau region covering 63 sites during January and February in 2018.A total of 184 snow samples were collected from this regions.The BC concentrations in snow cover were measured by SP2,and the spatial distribution characteristics and sources of BC in snow of typical snow area across northern China were analyzed by combining with enrichment factor and HYSPLIT-4 simulation backward trajectory.（1）In northern Xinjiang and the Tianshan Mountains region,the average concentrations of BC:Urumchi surrounding region(9.98 ng·g^-1)>the north slope of Tianshan Mountains(6.33 ng·g^-1)>Altay region(3.32 ng·g^-1)>Tahcheng region(3.10ng·g^-1)>the south slope of Tianshan mountains(1.64 ng·g^-1).The spatial distributions of BC in snow cover were in good agreement with the distributions of cities and industrial factories in this regions which around Urumqi and the north slope of Tianshan Mountains.Across Tahcheng area and Altay area,the BC concentrations were mostly between 0.71to 8.27 ng·g^-1in the snow pit and were between 0.29 to 15.72 ng·g^-1in the surface snow.The lowest BC concentration was 0.20 ng·g^-1at Chahannol Daban.（2）In the Northeast region,the average concentrations of BC:Xiaoxing’an Mountains surrounding region(56.55 ng·g^-1)>Changbai Mountain surrounding region(40.05 ng·g^-1)>Daxing’an Mountains region(6.45 ng·g^-1).The BC concentration in the Mohe region at the northernmost end of the sampling site was only 0.74 ng·g^-1.Across Xiaoxing’an Mountains and Changbai Mountain regions,the BC concentrations in surface snow,which were between 22.90～108.42 ng·g^-1,was significantly higher than that in the bottom layer due to industrial pollution and anthropogenic emissions.The BC concentrations of surface snow in the Northeast decreased as the latitudes increasing,which showed that the high concentrations of BC aerosols were deposited by precipitation within China and contributed little to atmospheric aerosols in Arctic.The fixed-point sampling analysis at Changbai Mountain Station every 7～8 days in the winter showed the BC concentrations in snow pits were decreacing with time and the average BC concentrations in the accumulation period（12.25～1.26）,the stable period（1.26～2.27）and the ablation period（2.27～3.15）were respectively 15.94,6.82,and 5.91 ng·g^-1.（3）Across the central and eastern Qinghai-Tibet Plateau region,the BC concentrations of snow layers were between 0.3 to 10.27 ng·g^-1.Among the six sampling points,the lowest value of BC concentrations in the snow pit was only 0.69 ng·g^-1and the highest value was 8.54 ng·g^-1and the average BC concentration in this region was3.22 ng·g^-1,which were comparable to those of Tahcheng area and Altay area and higher than that in the south slope of Tianshan mountains.In addition,the BC concentrations of fresh snow on the surface was lower than that on the bottom and the region suffered from serious snowdrift was more likely to have higher BC concentrations.（4）It was concluded that the AF of SO₄^2-and NO₃^-were as high as 99.74%and96.27%in typical snow area across the northern China.The concentrations of SO₄^2-,NO₃^-and BC showed the high concentrations of SO₄^2-and NO₃^-associated with anthropogenic emission of BC in industrial regions and densely populated cities,with much lower concentrations in suburban and mountains regions.The result of backward trajectory clustering showed that the northern Xinjiang and the Tianshan Mountains region was controled by westerlies and Local emissions and local pollution were the main sources of BC in snow.The Northeast region was mainly influenced by the northwest airflow from Siberia and long-distance exogenous input had great influence on BC concentrations in Daxing’an Mountains region.However,across Xiaoxing’an Mountains and Changbai Mountain regions,local industrial pollution and anthropogenic emissions could have significant impact on BC concentrations in snow.BC aerosols in the central and eastern Qinghai-Tibet Plateau mainly came from the west and southwest,which were dramatically influenced by South Asia,as well as by the Taklimakan desert.