Introduction to urban aerosols and their impacts

Atmospheric aerosols, or particulate matter, may be solid or liquid, with effective diameters from -0.002 to ∼ 100 μm. They can be emitted in particulate form directly into the atmosphere (primary aerosols) or formed in the atmosphere by chemical reactions of gases (secondary aerosols). Aerosol sources include mechanical processes such as grinding or wind erosion, gas-to-particle conversion of gas-phase primary pollutants, and combustion processes which occur primarily in urban centers. The impact of aerosols on the environment, human health, and climate depends on their number concentration, mass, size, chemical composition, phase (i.e. liquid or solid), morphology, and surface properties. Outlined in this Chapter is a brief overview of the physical and chemical properties of atmospheric aerosols as they relate to their to potential impacts on the environment and human health.