Long-Term Variation and Source Apportionment of Black Carbon at Mt. Waliguan, China

Black carbon (BC) is a significant driver of global climate change, and its long-term variation is affected by a combination of anthropogenic activities and meteorological diffusion conditions. However, distinguishing the effects of these two factors on BC variation has proven difficult. In this study, we used the China Black Carbon Observational Network data set to assess the diurnal, seasonal, and long-term BC trends at Mt. Waliguan (WLG) from 2008 to 2017. The mean BC concentration at WLG was 449 +/- 366 ng/m(3), with a decreasing trend of 2 %yr(-1), which was mainly related to emission reduction measures in China. The BC concentration at WLG was higher under easterly air masses than that under westerly air masses, which suggests that the former are conducive to BC transport from the highly polluted eastern regions. Due to the origin and velocity of air masses, the BC concentration at WLG in summer is higher than that in winter. The intensity of the Tibetan Plateau monsoon had an important positive influence on the easterly air masses frequency, 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 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.