title: Polycyclic aromatic hydrocarbon
context: Polycyclic aromatic hydrocarbons are primarily found in natural sources such as creosote.[13][14] They can result from the incomplete combustion of organic matter. PAHs can also be produced geologically when organic sediments are chemically transformed into fossil fuels such as oil and coal.[15] PAHs are considered ubiquitous in the environment and can be formed from either natural or manmade combustion sources.[16] The dominant sources of PAHs in the environment are thus from human activity: wood-burning and combustion of other biofuels such as dung or crop residues contribute more than half of annual global PAH emissions, particularly due to biofuel use in India and China.[17] As of 2004, industrial processes and the extraction and use of fossil fuels made up slightly more than one quarter of global PAH emissions, dominating outputs in industrial countries such as the United States.[17] Wildfires are another notable source.[17] Substantially higher outdoor air, soil, and water concentrations of PAHs have been measured in Asia, Africa, and Latin America than in Europe, Australia, the U.S., and Canada.[17]
question: What is the most common source of polycyclic aromatic hydrocarbons?
answers: creosote