Comparison of ultraviolet absorbance, chemiluminescence, and DOAS instruments for ambient ozone monitoring.

This paper evaluates the accuracy of ozone measurements made by monitors that determine ozone concentrations in ambient air by UV absorption. These monitors are typically used to measure ozone for the purpose of establishing local compliance to air-quality standards. The study was predicated by the concern that commercially available UV absorbance O3 monitors may be subject to interference from volatile organic carbon (VOC) species that absorb light at 254 nm. To test for these and other effects, we compared simultaneous O3 measurements made by a commercial UV O3 monitor with an O3-NO chemiluminescence instrument, which is not subject to interference by VOC compounds. The comparisons were carried out in the summers of 1999 and 2000 at urban/industrial sites in Nashville and Houston, and in 2004 aboard a ship in the Gulf of Maine. In the two urban areas, we also compared the 03 measurements from these two methods with O3 measurements made by a long-path differential optical absorption spectrometer (DOAS). Our tests indicate that, with well-maintained monitors, there are no significant interferences even in areas with significant ambient concentrations of potentially interfering VOCs.