Information on vapor-phase hydrocarbons presented in this document covers basic atmospheric chemistry relative to secondary products, especially ozone; sources and emissions; ambient air concentrations; relationship of precursor hydrocarbons to resultant ozone levels in ambient air; health effects; and welfare effects. The principal conclusions from this document are as follows. Hydrocarbons are a principal contributor to the formation of ozone and other photochemical oxidants; however, no fixed single quantitative relationship between precursor hydrocarbons and resulting ozone concentrations can be defined. This relationship varies from site to site depending on local precursor mixes, transport considerations, and meteorological factors. Consequently no single quantitative relationship can be defined nationwide. While specific hydrocarbon compounds can be of concern to public health and welfare, as a class this group of materials cannot be considered a hazard to human health or welfare at or even well above those concentrations observed in the ambient air.

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