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 similar to 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.

The climate effects of black carbon (BC) aerosols are sensitive to BC size distributions and this sensitivity over China is studied using a regional climate model, namely RIEMS2.0. A new size-resolved scheme is developed based on observational data. The simulated BC concentrations with the new scheme are better compared with the observation than the previous uniform scheme, which is likely to overestimate BC concentrations, radiative forcings, and warming effects in many regions of China due to its simple assumption on BC size. The simulation with the size-resolved scheme suggests a reduction of the all-sky radiative forcing of BC at the top of atmosphere (TOA) by 0-0.25 W m(-2) over the most study domain. Correspondingly, the warming effect of BC is weakened by -0.04 to -0.16 K over most parts of South China and North China. The difference in BC-induced precipitation between the two schemes varies irregularly from region to region, ranging from -2.8 to 2.8 mm d(-1). With the size-resolved scheme, the BC radiative properties and the climate effects are reassessed and the means (ranges) over the study domain are summarized as follows. The annual mean surface concentration of BC is 0.88 mu g/m(3), ranging from 1 to 8 mu g/m(3) over North China and Central China. The all-sky and clear-sky radiative forcings of BC at the TOA are 0.43 and 0.39 W/m(2), respectively. Over most parts of Southwest China, Central China, and North China, the BC warming effect prevails, with enhanced temperature of 0.04-028 K. BC aerosols usually enhance precipitation in South China and North China, ranging from 0.40 to 2.8 mm d(-1). (C) 2016 Elsevier B.V. All rights reserved.