Vertical Distribution Characteristics and Source Analysis of Heavy Metals in Near-Surface Urban Dust in Central Beijing

Urban dust serves both as a sink for heavy metals and a secondary source; however, its vertical distribution and source composition remain insufficiently explored. This study investigated the heavy metal concentrations in rooftop and ground dust samples collected from Haidian District, Beijing. Using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and receptor models (PCA and APCS-MLR), we analyzed the spatial variation, pollution levels, ecological risks, and source apportionment of eight heavy metals (V, Cr, Ni, Cu, Zn, As, Cd, Pb). The results indicated that rooftop dust exhibited generally higher concentrations and ecological risks, with cadmium identified as the most critical pollutant. APCS-MLR analysis revealed that rooftop dust was predominantly influenced by an unidentified source (67.4%), whereas ground dust was mainly affected by combustion sources (42.4%) and traffic emissions (18.2%). This vertical heterogeneity suggests that rooftop dust primarily reflects regional atmospheric deposition, while ground dust captures local pollution signals. These findings underscore the necessity for three-dimensional environmental monitoring and targeted pollution control strategies in urban areas.