An aerosol is a colloidal system consisting of a solid or liquid particles suspended in a gas phase. Ubiquitous in numerous areas of science, aerosol play a key part in daily life for their use in the application of cosmetics, deodorants and paints, in the delivery of drugs, the dispersion of pesticides and air fresheners etc., and are important in industrial processes, such as in the delivery of fuels for combustion and spray drying to produce powders. Perhaps the most significant influence aerosol have on day-to-day life comes from their effect on climate and weather due to their role in cloud formation. The importance of aerosol in the atmosphere extends to their interactions with solar radiation and their influence on ozone concentrations and on the formation of acid rain. The impact of aerosol in highly polluted areas is of great importance due to the negative impact of inhaled particulate matter on health and their effect on visibility.
Aerosol also represent a unique state of matter due to the very high surface-to-volume ratios, increasing the importance of interfacial effects, such as enhanced partitioning of surface active species. Adsorption of species to this interfacial region may significantly alter the kinetics of certain bimolecular reactions, as confinement effects can change the potential energy landscape of a reaction. The formation of supersaturated solution droplets and the associated high chemical activity of solutes can also drive chemistry in directions not typically encountered in bulk solutions.