Aerosols are colloids of tiny solid or liquid particles suspended in the atmosphere. Their diameters typically range between 0.001 and 100 μm. Aerosols are recognized as a major factor influencing global and regional climate change owing to their ability to scatter and absorb solar radiation. Indirectly, they modulate Earth’s energy balance by altering cloud properties—in particular, cloud droplet size—by serving as cloud condensation nuclei, which further influence the cloud fraction, height and lifetime. All these aspects result in modification of the planetary albedo and hydrological cycle. Some important environmental issues, such as haze, acid rain and tropospheric ozone pollution, are also closely correlated with aerosol pollution.