The main change in the atmospheric composition is primarily due to the combustion of fossil fuels, used for the generation of energy and transportation. Variant air pollutants have been reported, differing in their chemical composition, reaction properties, emission, persistence in the environment, ability to be transported in long or short distances and their eventual impacts on human and/or animal health. However, they share some similarities and they can be grouped to four categories:
1.Gaseous pollutants (e.g. SO2, NOx, CO, ozone, Volatile Organic Compounds).
2.Persistent organic pollutants (e.g. dioxins).
3.Heavy metals (e.g. lead, mercury).
4.Particulate Matter.