This review has established that the characterization of aerosol particle size is a complex task, with no single methodology serving all purposes. The choice of an appropriate technique must be guided by the size range of interest, the information required (e.g., number vs. mass distribution), and a clear understanding of the physical principle behind the measurement. Based on the analysis presented, the following guidance can be offered to the professional seeking to measure aerosol size distributions.

• For real-time number concentration of particles larger than ~0.1 µm, optical methods like light-scattering particle counters are highly effective. However, users must remain aware of the strong influence of particle refractive index on sizing accuracy, especially when analyzing aerosols of unknown or variable composition.
• For determining mass-based size distributions of particles generally larger than 0.5 µm, inertial methods, particularly the cascade impactor, are the standard approach. To ensure data quality, it is essential that the experimental setup includes strategies to mitigate artifacts such as particle bounce.
• For high-resolution sizing of sub-micron and ultrafine particles (from ~0.002 to 0.5 µm), the Electrical Mobility Analyzer is the principal technique. It is uniquely suited for this range because it leverages a fundamental electrical property to classify particles that are too small for effective inertial separation and too small for unambiguous optical detection.

Ultimately, the accurate characterization of any aerosol system hinges on this foundational knowledge. A thorough understanding of the principles, measured parameters, and inherent limitations of each method is not just beneficial—it is essential for generating reliable and meaningful data.