Unveiling differences in source apportionment and optical properties of wintertime carbonaceous aerosols in northern and southern Chinese Cities

Carbonaceous aerosols adversely affect air quality, visibility and public health. Understanding their regional variations and sources in China is essential for improving air quality control. Carbonaceous aerosols were collected during winter in four major Chinese cities—Xi'an (XA), Shijiazhuang (SJZ), Wuhan (WH), and Chongqing (CQ)—to investigate their pollution characteristics. A comprehensive analysis of various carbon fractions was conducted, including organic carbon (OC), elemental carbon (EC), and specific subfractions such as OC1 – OC4, EC1 – EC3, char-EC, and soot-EC. Using the hybrid environmental receptor model (HERM), we identified emission sources and quantified their contributions to primary total carbon (PTC) in these urban areas. The findings demonstrate substantial impacts from coal combustion during the heating season in XA and SJZ. Vehicular emissions account for a considerable proportion, particularly in SJZ, corresponding with the increase in automobile ownership in that city. In WH and CQ, emissions from industrial and residential coal utilization, especially from the steel industry, are markedly higher. Additionally, the COVID-19 pandemic results in reduced contributions from industrial emissions in WH and SJZ. We further investigate the optical characteristics of EC, revealing that the average mass absorption efficiency (MAE) values across the four cities are consistent with previous studies. Specifically, MAEs derived from different emission sources indicate higher values from biomass burning and stationary combustion in XA and CQ, whereas industrial sources result in elevated values in SJZ and WH. This study delineates the distinct characteristics of carbonaceous aerosols in northern and southern Chinese cities, providing a robust scientific basis for urban air pollution mitigation strategies.