Non‐Volatile Particulate Matter as Cores Driving Aerosol Mixing States and Light Absorption

Abstract The mixing state of light‐absorbing particles critically influences aerosol optical properties, thereby affecting global radiative forcing. This study focuses on non‐volatile particulate matter (NV‐PM)—the fraction remaining after thermal denudation at 300°C—has received limited attention. Using observations in Shanghai, we show that ambient aerosols exhibit a bimodal size distribution, with the larger mode strongly correlated with NV‐PM ( R 2 ∼ 0.83), suggesting that NV‐PM acts as seed particles. We propose an S/L‐mode mixing‐state classification that separates small and large diameter modes and apply a core–shell optical model using retrieved refractive indices for NV‐PM and coatings. Modeled absorption at 530 nm agrees with observations and reproduces the mean absorption enhancement ( E abs ∼ 2.80 vs. 3.28 observed). Our analysis attributes about one‐third of absorption to brown carbon. This work advances the understanding of aerosol mixing state and absorption mechanisms, supporting more accurate estimates of aerosol radiative forcing in climate models.