Roof dust accumulation characteristics and influencing factors in typical urban areas of Beijing

Understanding roof dust and its environmental drivers is essential for interpreting urban particulate dynamics. We collected 159 roof- and ground-dust samples across a university campus in central Beijing (December 2020-November 2021) as a representative urban setting to examine vertical and seasonal patterns. Dust mass, PM₁₀ and PM_2.5 concentrations were analyzed against meteorological conditions. Clear seasonality emerged, with dust mass peaking in February-March and reaching minima in summer-autumn. PM₁₀ correlated strongly with total dust mass (r = 0.773), indicating a prominent coarse-particle contribution to rooftop deposition. Sectoral winds modulated accumulation: southeast and south-southwest flows enhanced dust loading, whereas north-northwest winds suppressed it. A wind-speed threshold was observed, with rooftop loads increasing above ~ 2.5 m s^-1 and strongest accumulation at > 5 m s^-1. Precipitation frequency and relative humidity were inversely related to dust mass (r = - 0.755 and - 0.773), consistent with wet removal and reduced resuspension. A multivariate synthesis (PCA/PCR) further shows that a high-RH, warmer and low-wind composite state is significantly and negatively associated with roof dust, supporting denser roof sampling and cleaning during dry, windier periods and highlighting roof deposition as a complementary urban monitoring metric. Roof dust accumulation generally decreased with increasing building height, although unexpectedly high dust loads were observed on mid-rise buildings, likely due to higher building density and restricted local air circulation. These findings demonstrate that roof dust accumulation is strongly modulated by seasonal meteorology, wind regimes, and urban morphology. The vertical distribution patterns identified here provide a basis for integrating roof sampling into urban air quality monitoring and for refining models of particulate dispersion in dense cityscapes.