Abstract: Black carbon (BC), emitted from anthropogenic activities and wildfires, strongly absorbs solar radiation and is recognized as a sensitive indicator of climate and environmental change． In sparsely populated remote areas, however, whether restrictions on human activities can significantly alter ambient BC concentrations and thereby improve air quality remains poorly understood． Based on BC observations at a background site in Jimunai County, located in the northwestern border region of China, this study selected two representative periods (lockdown and non-lockdown periods) to investigate the variations in carbonaceous aerosols under different levels of anthropogenic activity． The results show that during the lockdown period, the BC concentration at the Jimunai background site decreased significantly from 0.47 µg·m⁻³ to 0.23 µg·m⁻³, representing a reduction of 51%． Model analysis indicates that the variations in observed BC concentrations before, during, and after the lockdown are generally consistent with meteorologically normalized concentrations, suggesting that meteorological conditions had a limited influence on BC levels during the lockdown, and that the observed changes were mainly driven by variations in anthropogenic emissions． Analysis of wind field observations further reveals that BC variations during the lockdown were primarily influenced by anthropogenic emissions from the upwind Jimunai region． In addition, despite the implementation of lockdown measures, BC concentrations in the autumn–winter period of 2019-2020 remained higher than 2023-2024． Concentration-weighted trajectory (CWT) analysis further shows that the dominant source regions of long-range transport were located to the west of the observation site in 2019-2020, but shifted to the northwest in 2023-2024． The spatial differences in upwind BC source regions may account for the discrepancies between the two periods．