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Evaluation and Comparison of Chemiluminescence and UV Photometric Methods for Measuring Ozone Concentrations in Ambient Air
Long, R., M. Beaver, R. Duvall, EricS Hall, S. Kaushik, K. Kronmiller, M. Wheeler, AND S. Garvey. Evaluation and Comparison of Chemiluminescence and UV Photometric Methods for Measuring Ozone Concentrations in Ambient Air. In Proceedings, 2015 (108th) A&WMA Annual Conference, Raleigh, NC, June 22 - 25, 2015. Air and Waste Management Association, Pittsburgh, PA, 546, (2015).
The National Exposure Research Laboratory’s (NERL’s) Human Exposure and Atmospheric Sciences Division (HEASD) conducts research in support of EPA’s mission to protect human health and the environment. HEASD’s research program supports Goal 1 (Clean Air) and Goal 4 (Healthy People) of EPA’s strategic plan. More specifically, our division conducts research to characterize the movement of pollutants from the source to contact with humans. Our multidisciplinary research program produces Methods, Measurements, and Models to identify relationships between and characterize processes that link source emissions, environmental concentrations, human exposures, and target-tissue dose. The impact of these tools is improved regulatory programs and policies for EPA.
The current Federal Reference Method (FRM) for measuring concentrations of ozone in ambient air is based on the dry, gas-phase, chemiluminescence reaction between ethylene (C<SUB>2</SUB>H<SUB>4</SUB>) and any ozone (O<SUB>3</SUB>) that may be present in air samples. Although technically sound, currently this method is seldom used nor is it readily available or supported commercially. The most widely used method for measuring ozone is the Ultraviolet (UV) photometric method which is a Federal Equivalent Method (FEM). However, this method is prone to interference from water vapor, volatile organic compounds (VOCs) and other compounds existing in ambient air that absorb in the UV spectrum. Two newly introduced and recently designated O<SUB>3</SUB> FEM analyzers have the potential to eliminate the shortcomings of both the ethylene-chemiluminescence (ET-CL) reference method and the widely used UV photometric methods. The first utilizes Nitric Oxide-chemiluminescence (NO-CL) to measure ozone in the atmosphere where the reaction between ambient ozone and NO produce light proportional to the ozone concentration. The second represents a variation of the UV photometric method, known as the “scrubberless” UV (SL-UV) method that specifies removal of O3 from the sample air for the zero reference by a gas-phase reaction with NO rather than via a conventional solid chemical scrubber. Both methods, either through measurement principle, or sample treatment processes may effectively eliminate interferences to an insignificant level. The EPA performed research on FRM and FEM methods for the measurement of ozone in both laboratory and ambient settings. The laboratory based evaluation results presented in this manuscript indicate that the majority of the methods and analyzer types investigated, are capable of meeting the current and proposed revised performance specifications, per 40 CFR Subpart B, for new FRM and FEM analyzers. The results of five ambient based evaluations and comparisons of existing FRM and FEM analyzers for ozone generally show good agreement among the methods for one-hour average and maximum daily eight-hour average ozone concentrations. The results of this research will play an informative role in the National Ambient Air Quality Standard (NAAQS) review process for ozone and the measurement methods used for its regulatory determination.