In this illustration, the structure of polycyclical aromatic hydrocarbons (PAH) is shown. These are present in smoke
of various types, including wood smoke and tobacco smoke. Notice the "notched" ring structure. This is generated
via pyrolysis of biomass cellulose. A burning wood log generates a higher amount of PAH than smaller tobacco grains,
due to the low volume to surface area ratio of the fuel.
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source: General, Organic, and Biological Chemistry, H. Stephen Stoker, Houghton-Mifflin, 2004
