Water is one of the main atmospheric components, present in the form of vapour, rain, cloud, fog droplets, and deliquescent atmospheric aerosols (hygroscopic aerosol at high humidity). The presence of a liquid water phase in the atmosphere promotes reactions that would not occur otherwise. One important class of reactions is complexation of metals by organic ligands.
Coordination chemistry is important for both the Earth's climate and public health. As coordination chemistry happens, the physical properties of the atmospheric particles may change such as their optical properties, thus influencing their ability to interact with solar radiation, and hygroscopical properties, thus influencong their ability to interact with clouds. When metal ions are coordinated with organic compounds their solubility changes as well as their potential to cause oxidative stress in the human lung once the particles are inhaled.