Tropospheric pollution is caused by gaseous air pollutants as well as particulate pollutants. Among the gaseous air pollutants, oxides of sulphur $(SO_x)$, oxides of nitrogen $(NO_x)$ and carbon monoxide play an important role towards pollution. Formation of acid rain and photochemical smog, greenhouse effect and global warming all are the result of various chemical and photochemical reactions taking place in the environment. Various particulates including viable and non-viable are also responsible for causing serious air pollution.
The aromatic compounds present as particulates are