In-Tandem Multi-Waveband Particulate Absorption and Size Observations Yield Substantial Increase in Radiative Forcing over Industrial Central China

Abstract. Coal-based industry in Shanxi, China, including power generation, steel, coke, and chemical manufacturing, emits large quantities of black carbon (BC), contributing significantly to regional aerosol radiative forcing. However, there are substantial scientific uncertainties in the radiative properties of the aerosols in these types of regions due to multiple sources of BC and high emissions of co-emitted aerosol precursors, producing mixed aerosols of different ages, sizes, and morphologies. This study combined optical particle size and multi-band in-situ BC mass and column aerosol optical depth, with MIE modeling to simulate optical properties per particle and over the atmospheric column for absorbing aerosols. These results are applied in a radiative transfer model to constrain regional radiative forcing. First, BC shows a trimodal fine-mode (size<2.5 μm) size distribution, substantially differing from current assumptions of aerosol size made by satellite and atmospheric modeling communities. Second, the coating ratio between absorbing-core and refractive-shell varies dynamically, challenging the widely used fixed mixing ratio assumption. Thirdly, absorbed solar radiation under 500 nm is weaker than from 500 to 700 nm, and weaker still than above 800 nm, challenging assumptions of flat or decreasing absorption with radiative band. Our results yield a reduced single scattering albedo (-0.049 to -0.008) and substantial change in column number (-1.73×1012 to 5.74×1010 # m-2), resulting in radiative forcing from 0.3 to 3.0 W m-2, surpassing local CO2 and CH4 forcing. This work provides a realistic probabilistic framework to quantify BC aging and mixing induced optical properties in industrial regions.