Aerosols are tiny particles present in the atmosphere.
There are many different types of particle including soot, sulphuric acid and ammonium sulphate droplets, organic droplets, mineral dust, sea-salt and volcanic ash. Aerosols can affect climate since they can scatter and absorb solar radiation and, in some cases, infra-red radiation emitted by the Earth. Additionally, aerosols can alter the microphysical properties of clouds, making them brighter or longer lasting. Aerosols can also provide sites for heterogeneous chemical reactions in the atmosphere. Currently, our understanding of past climate change and our ability to predict future climate change is hampered by our lack of understanding of aerosol composition and radiative impact.