The problems of air pollution and global warming are linked to changes in the chemical composition of the atmosphere and depend not only on emissions of gases and particles, but also on their fate into the atmosphere. In order to effectively combat the various forms of pollution, it is essential to understand the physico-chemical mechanisms involved and to carry out precise measurements of the concentrations of the various constituents of the air (gaseous and particulates). These data feed into predictive models of air quality and chemical composition of the atmosphere. The atmospheric fate of gaseous pollutants emitted directly or generated into the atmosphere depends largely on the levels of hydroxyl radicals (OH) by day and nitrate radicals (NO3) at night. These radicals are highly reactive and are responsible for initiating the degradation processes of primary and secondary pollutants, leading to the formation of high health impact pollutants such as ozone (O3), aldehydes, secondary organic aerosols (AOS) and other harmful pollutants. The formation of aerosols and the degradation of greenhouse compounds such as hydrofluorocarbons and methane during degradation reactions initiated by OH alter the radiative balance of the planet and contribute to climate change...