Hydrocarbons
Hydrocarbons can occur in various forms in the exhaust gases. Their odor can be different (aromatic or pungent). In high concentrations, some hydrocarbons can have a narcotic effect while others can irritate the mucous membranes. Depending on their nature, they are more or less toxic. Benzene, an aromatic hydrocarbon, is classified as carcinogenic. Hydrocarbons have a major importance in smog formation.