A Study On The Spatiotemporal Distribution Of Black Carbon Aerosols In China And Its Influencing Factors At Hualiguan Station

Black carbon（BC）is a significant driver of global climate change,and its long-term variation is affected by a combination of human activities and meteorological diffusion conditions.However,distinguishing the effects of these two factors on BC variation has proven difficult.In this study,using the data from the China Black Carbon Observation Network,we study the temporal and spatial distribution characteristics and source analysis of BC across China,and analyze the impact of meteorological conditions on BC.In addition,taking Mt.Waliguan（WLG）as an example,assess the characteristics and influencing factors of the diurnal,seasonal,and long-term BC trends from 2008 to 2017.The contributions from potential BC source regions were identified through concentration-weight trajectory analysis and quantified by CAM5 with the BC-tagging technique.In addition,we analyzed the Tibetan Plateau monsoon index to explore its influence on easterly frequency and the regional transport of BC to WLG.The results are shown as follows:1)Spatial and temporal distribution of BC in China and its influencing factorsThe concentration of BC in China has shown a decresing trend as a whole.The BC concentration of the eastern site was significantly higher than that of the western site,and the BC concentration of the urban site was higher than that of suburban sites and atmospheric background sites.On the whole,BC has a more obvious positive correlation with SO₂ and NO₂,the BC concentration has a higher correlation with the NO₂ concentration.The variation of BC and PM_2.5 is the same.The proportion of PM_2.5 and BC/CO value of urban site BC is higher than that of suburban sites.The urban site BC is more affected by liquid fuel emissions.The influence of wind speed and precipitation on BC concentration is greater than the maximum temperature and relative humidity.Low humidity is favorable for BC growth,and high humidity is conducive to BC removal.2)Long-term variation and source apportionment of black carbon at Mt.Waliguan,ChinaThe mean BC concentration at WLG was 449±366 ng/m³,with a decreasing trend of2%yr^-1,which was mainly in response to emission reduction measures in China.The BC concentration at WLG was higher under easterly wind than under westerly wind,which suggests that easterly wind is conducive to BC transport from the highly polluted eastern regions.The BC concentration at WLG was therefore higher in summer than in winter due to the highest easterly frequency in summer.The intensity of the Tibetan Plateau monsoon had an important positive influence on the interannual variation of easterly frequency at WLG,which modulated BC transport to WLG in summer.According to the concentration-weighted trajectory analysis,the high potential BC source regions were distributed in Lanzhou,Chengdu,and Xi’an urban agglomerations as well as in northern India.Community Atmosphere Model 5（CAM5）simulations with a BC-tagging technique inferred North Central China,Northwest China,and Indian Peninsula to be the major BC source regions to WLG,accounting for 56.1%,17.5%,and 12.1%of the total BC,respectively.