A New Methodology for Evaluating Ozone Production Rate Instruments

Tropospheric ozone (O₃), the third most important greenhouse gas, has harmful effects on human health, vegetation and climate. Indeed, increases in O₃ are associated with a higher risk of respiratory illnesses, and significant impacts on crop yields have been reported.The formation chemistry of tropospheric ozone is complex and nonlinear, involving photochemical reactions driven by nitrogen oxides (NO_x = NO + NO₂) and volatile organic compounds (VOCs). Locally, the O₃ budget is governed by advection, net local production, and dry deposition. To identify the major production pathways contributing to the net local production rate, P(O₃), and distinguish it from advected O₃ pollution, a technology capable of monitoring P(O₃) has been developed. This instrument is referred to in the literature as Measurement of Ozone Production Sensor (MOPS) or Ozone Production Rate instrument (OPR).

Before field deployment, the performance of this type of instruments must be tested to ensure its reliability and accuracy. In this study, we present an evaluation methodology developed to assess the performance of an OPR instrument. We demonstrate how a small gas-generation unit, capable of providing synthetic air mixtures of VOCs and NO_x to the OPR, can be combined with a lamp-based irradiation system covering the OPR to evaluate its performance. In this approach, the ozone production rate P(O₃) within the OPR is simulated using the Framework for 0-D Atmospheric Modeling (F0AM), an open-source MATLAB-based box model. We present laboratory tests of the IMT OPR instrument under various controlled conditions spanning ozone production regimes from NO_x-limited to NO_x-saturated. The reliability and limitations of this combined experimental–modeling approach and the performance of the IMT OPR instrument are discussed.

Acknowledgments. This work was performed as part of the OSEAMS project, funded by the French national agency (ANR) and the National Science and Technology Council (NSTC).