Size‐Resolved Microphysical and Optical Properties of Atmospheric Aerosols in an Urban Area of the Northern Tibetan Plateau

Abstract Aerosols over the Tibetan Plateau (TP) strongly influence regional climate and hydrological cycles. Here we investigate the size‐resolved microphysical and optical properties of aerosols in an urban area of the northern TP using a tandem system of a differential mobility analyzer, a condensation particle counter, and a single particle soot photometer. Under the 2021 summer conditions, the average particle number size distribution follows a lognormal pattern, peaking at ∼70 nm. Refractory black carbon (rBC) aerosols constitute 17.7% of the total particle population in the 100–750 nm mobility diameter ( D mob ) range, with their proportion rising to over 50% for D mob > 500 nm. Most rBC particles are externally mixed, while only 12.2% are thickly coated with non‐refractory materials. Externally mixed rBC particles show strong non‐sphericity, with a dynamic shape factor increasing from 1.8 at 115 nm to 2.8 at 750 nm, consistent with aggregate structures. In contrast, thickly coated rBC particles are nearly spherical, with coating thickness increasing with size. The total rBC mass estimated from size‐resolved measurements closely matches bulk rBC mass directly measured. rBC‐free particles exhibit slight non‐sphericity, with shape factor positively correlated with refractive index, likely due to dust contributions. Bulk scattering coefficients derived from size‐resolved data match those estimated under the well‐mixed spherical assumption. However, the later scheme—lacking observational constraints on morphology and mixing state—overestimates absorption by over a factor of three, thereby underestimating the single‐scattering albedo. These results provide key constraints for improving aerosol radiative forcing estimates and advancing understanding of aerosol–climate interactions over the TP.