①Benzene hydrocarbons or monobenzene aromatic hydrocarbons, compounds with one benzene ring and their derivatives. Such as benzene, phenol, halogenated benzene, toluene, etc.；
②Polycyclic aromatic hydrocarbons (PAH), polycyclic hydrocarbons with benzene ring or heterocyclic ring shared edge. Such as naphthalene, anthracene, perylene, benzopyrene and so on.
For example, polycyclic compounds formed by two or more benzene rings and heterocyclic rings sharing ring edges are called benzene fused heterocyclic compounds, such as indole, quinoline, fluorene and so on.Emissions from industries such as coking, petrochemicals, dyes, pharmaceuticals, pesticides, paints, and fossil fuel combustion are the main man-made sources of aromatic hydrocarbons in the environment. Some plants and bacteria in nature can also produce such compounds, such as eugenol and wintergreen oil. Many aromatic hydrocarbons are harmful substances in the environment, especially the pollution of polycyclic aromatic hydrocarbons can cause mutagenicity and carcinogenicity, which has attracted worldwide attention.