Polyaromatic hydrocarbons are thought to be extremely old compounds, with essential roles in the formation of stars, planets and possibly life itself. However, they are also extremely toxic to humans, and are present in countless shapes and forms all around us, from wood smoke and cigarette smoke to vehicle exhaust.
Polyaromatic hydrocarbons (also known as polycyclic aromatic hydrocarbons or polynuclear aromatic hydrocarbons) are organic compounds made up of carbon and hydrogen. Under various combinations, they can form more than 100 chemicals, all of which are toxic in certain amounts and to certain degrees. (The term "aromatic" as used in chemistry has nothing to do with its common layman use, and refers to certain stable organic ring-shaped molecules.) PAHs can occur naturally or be man-made.
While PAHs usually occur unintentionally, and therefore usually have no "uses" as such, they are employed to a certain extent in various industries:
PAHs are among the most common pollutants throughout human history, because they occur naturally as a result of many basic human activities. The most widely encountered PAH-producing activity in older times was cooking on a wood-burning stove or grill, and heating houses through wood burning activities.
In more recent times, there are other powerful PAH pollutants as well:
Depending on the regulations enforced in each country, some of these PAH pollution factors are better controlled. In poorer countries, with lower levels of enforcement, PAH pollution is more severe. This is worrying, as some PAHs are known carcinogens. Exposure to high levels, for instance when breathing coal tar vapors or otherwise being exposed to large quantities of various PAHs, can cause: