Temporal Variation Characteristics, Sources and Influencing Factors of Black Carbon Aerosol in Shouxian, Anhui Province

Black carbon (BC), the most important light-absorbing component of atmospheric aerosol, has a significant impact on global climate change, atmospheric environment and human health. Based on the observed data of BC concentration in Shouxian, Anhui Province, from March 2023 to February 2024, combined with the atmospheric pollutant concentration and meteorological factors data during the same period, this study systematically analyzed the temporal variation characteristics and sources of BC in rural areas of the Yangtze River Delta. The results showed that the annual average concentration of BC is (0.88±0.59) μg/m3, showing a seasonal variation characteristic of ″high in autumn and low in summer″, as well as monthly variation characteristics with the highest in October and the lowest in July, which primarily due to the seasonal differences of emission sources and meteorological conditions. Influenced by the diurnal variation of meteorological factors and the human activities patterns, BC concentration showed a distinct bimodal diurnal pattern, with peaks at 6:00-8:00 AM and 18:00-20:00 PM. The bimodal peaks were the highest in autumn and lowest in summer. The morning peak exceeded the evening peak in spring and summer, and opposite in autumn. The morning peak time was the earliest in summer and the latest in winter, and the evening peak time was opposite. The source apportionment results based on Aethalometer model indicated fossil fuel combustion (BCff) was the dominant source, accounting for 74.4% of BC, while biomass burning (BCbb) contributed 25.6% on average. BCbb exhibited more pronounced seasonal variations than BCff, contributing the most in winter (34.3%) and the least in summer (17.4%). The Random Forest model was used to analyze the influencing factors of BC, and it was found that boundary layer height (BLH), nitrogen dioxide (NO2), air temperature (t) and carbon monoxide (CO) were the four most critical factors. BC concentration decreased with increasing BLH and increased nonlinearly with rising NO2 and CO. Under low temperature conditions, BC and BCff showed a positive phase change with t, while under high temperature conditions, BCbb showed an inverse phase change with t. This model effectively elucidated the relationship among pollution emissions, meteorological conditions and BC concentrations, providing a scientific basis for the management and control of atmospheric BC pollution.