Deciphering the Sub-Particle Structural Control on Optical Properties of Complex Aerosols Containing Microplastics via the GMM Method

Atmospheric aerosol radiative forcing remains a significant uncertainty in climate models, partly due to oversimplified representations of complex aerosol structures. Here, we employ the generalized Mie method to quantify the optical properties of aerosol clusters containing black carbon (BC), dust, and microplastics (MPs) in triangular and fractal configurations. We demonstrate that sub-particle arrangement and size distribution are critical drivers of optical variability. Across 300–1100 nm, fractal clusters (20 sub-particles) exhibit extinction cross-section variations up to 2.8-fold and scattering cross-section differences of 60%, primarily governed by compositional heterogeneity and size dispersion. While ensemble averaging stabilizes scattering cross-sections (>18 samples), persistent fluctuations in extinction cross-sections due to size heterogeneity challenge the reliability of extinction-based equivalent coefficients. Our results underscore that remote sensing retrievals prioritizing scattering cross-sections exhibit superior robustness compared to extinction-based methods. This work establishes unresolved structural complexity as a fundamental constraint in aerosol optics and advocates for a paradigm shift towards scattering-based inversion frameworks to reduce uncertainties in climate prediction.