A review of measurement techniques for aerosol effective density

Density (ρ) is one of the most important physical properties of aerosol particles. Owing to the complex nature of aerosols and the challenges of measuring them, effective density (ρ_e) is generally used as an alternative measure. Various methods have been developed to quantify the ρ_e of aerosols, which provide powerful technical support and understanding of their physical properties. Here, we present a comprehensive review of the characterisation techniques of ρ_e currently used in the literature. Overall, six categories of measurement are identified, and the typical configuration, measurement principles, errors and field applications of each are demonstrated. Their respective advantages and disadvantages are also discussed to improve their application. Finally, we outline future directions for further technical improvement in, and instrumental development for, ρ_e measurement.