Aerosol mixing state revealed by transmission electron microscopy pertaining to cloud formation and human airway deposition

Abstract Aerosol mixing state is one of the most important factors determining the impacts of aerosol particles on aerosol-cloud-climate interactions and human health. The size, composition, and morphology of about 32,000 single particles are analyzed using transmission electron microscopy (TEM) to evaluate per-particle mixing state. Based on the TEM analysis, we quantify aerosol mixing state and examine the impacts of per-particle mixing state on cloud condensation nuclei (CCN) properties and particle deposition efficiency along the human respiratory tract. Assuming homogeneous chemical composition across the aerosol population, a common practice in many global and regional models to various extents, we show that such simplification of mixing state representation could potentially lead to remarkable errors, a maximum of about 90% and 35%, in CCN concentrations and deposition efficiency calculations respectively. Our results from ambient per-particle observations highlight the importance of considering aerosol mixing state in both air quality models and climate models.