Final answer:
The pollutant typically characterized by size is particulates, a form of pollution that includes various substances but is categorized by the size of the particles.
Step-by-step explanation:
The pollutant usually described by size rather than composition is particulates. Particulate matter, also referred to as particle pollution, includes a variety of components such as acids (like nitrates and sulfates), organic chemicals, metals, and soil or dust particles.
The size of these particles is a crucial factor because it determines how the particles affect human health and how deep they can penetrate into our respiratory system. The Environmental Protection Agency (EPA) is particularly concerned about particles that are 10 micrometers in diameter or smaller, as they can pass through the throat and nose to enter the lungs, potentially causing serious health effects.