Ozone precursor monitor for investigating air pollution

Ozone is designated by the Environmental Protection Agency as one of six principal air pollutants. Of the six, ozone alone is classified as a secondary pollutant since it is not emitted by a specific source. Ozone is formed in the lower atmosphere by photochemical reactions involving the precursors of ozone: gaseous organic compounds (mostly hydrocarbons), nitric oxide, and nitrogen dioxide. This paper describes a new automated method for quantifying the precursors of ozone. An ozone analyzer is coupled to a reaction vessel contained in an irradiation chamber. At timed intervals discrete samples of outside air are drawn into the reaction vessel and irradiated with ultraviolet light. The amount of ozone produced is a measure of the photochemical reactivity potential of the precursor blend. The ozone precursor monitor (OPM) is designed for urban air sampling stations where analyzers for the principal air pollutants are routinely operated. The monitor, however, has other uses. Among special applications of the method that are discussed are its use as an early warning device for forecasting elevated ozone concentrations, a screening system for assessing the photoreactivity of solvents, and a procedure for investigating the transport of ozone precursors from urban to rural areas.