Nonmethane hydrocarbons photochemical oxidation

For the measurement of the hydrocarbon precursors of photochemical oxidants, the naturally occurring methane must be separated from the other so-called nonmethane hydrocarbons. Only one procedure, gas chromatography coupled with flame ionization detection, is available for this separation and measurement. Although instrumentation for routinely accomplishing this process is commercially available, its maintenance (continued operation) requires a degree of operational know-how that may be too costly for most public agencies in the United States to support. Consequently, the data currently are insufficient to relate the occurrence of photochemical oxidants and ozone accurately to some of their most important precursors, the nonmethane hydrocarbons. 

Nonmethane hydrocarbons and both oxides of nitrogen should be monitored concurrently whenever photochemical oxidant or ozone is monitored. 

NAAQS), for the identified criteria pollutants. At that time, six ubiquitous air pollutants were designated as criteria pollutants photochemical oxidants (which later became ozone), sulfur dioxide, nonmethane hydrocarbons (which was later dropped as a criteria air pollutant), nitrogen dioxides, carbon monoxide, and total suspended particulates. Lead was later added as a criteria pollutant. 

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