<b>Multi-platform observations and constraints reveal overlooked urban sources of black carbon in Xuzhou and Dhaka</b>

Here we use multi-waveband single scattering albedo data from ground-based and space-borne remote sensing platforms, to optically constraint and characterize black carbon aerosol size and mixing state, over,Xuzhou, China, and Dhaka, Bangladesh. Our findings reveal smaller black carbon cores and non-linear morphological changes in both regions. Computed column concentrations reveal higher black carbon column mass in Dhaka, while, Xuzhou exhibits greater total column mass and number concentration, reflecting differences in emissions sources, atmospheric conditions, and regulatory policies. Spatial analysis reveals notable black carbon loading along Dhaka's urban riverbanks (8-9 mg m^-2), and in rapidly growing lower-tier cities and small industrial sites in China, indicating overlooked sources. Complex interactions between wind patterns, aerosol accumulation, and dispersion challenge traditional seasonal dynamics. These findings demonstrate high-resolution data can be tailored from available remote sensing platforms, providing nuanced insights into regional air quality, enhancing assessment capabilities and informing targeted mitigation strategies.