This chapter mainly focuses on regulated gaseous air pollutants, introducing the concepts for their formation and measurements. It presents alongside, where applicable, the trends showing contribution from different natural and anthropogenic sources. Natural gas, which is mainly the simplest hydrocarbon methane, is associated with both the formation of coal seams and oil deposits. The three major groups of gaseous air pollutants by historical importance, concentration, and overall effects on plants and animals are sulphur dioxide, oxides of nitrogen and ozone. The emission is dependent on the conditions of combustion, in particular temperature and excess air ratio, which can vary considerably. In atomic emission spectroscopy, atomic collisions due to the high temperature of the sample knock electrons into higher energy states from which they subsequently decay with the emission of a photon. Ammonia emissions can be changed by feed N content, the conversion of feed N to meat N and the management practices applied to the animals.