Direct evaluation of the ozone production regime in smog chamber experiments

Understanding the atmospheric ozone (O3) production regime is necessary for development of strategies to effectively control the amount of atmospheric O3. We have developed an instrument to directly evaluate the O3 production regime by measuring incremental changes of O3 production rate after injection of nitric oxide and propene into sample air. In this study, we conduct smog-chamber experiments on the oxidation of nitrogen oxides (NOx) and volatile organic compounds (VOC) and use the above instrument to measure O3 production during air mass oxidation. We also perform box model simulations with two chemical mechanisms (one near-explicit and one lumped) to cross validate the measured and simulated O3 production regimes. Oxidation experiments are conducted under VOC-rich and NOx-rich conditions; and the simulation generally reproduced O3 concentrations, OH reactivity (OHR), and contribution of NOx to total OHR. The measured O3 production regime changed from VOC-limited to NOx-limited after 1–3 h of irradiation by xenon arc lamps under the VOC-rich condition, whereas the regime remains VOC-limited throughout our experiment under the NOx-rich condition. The simulated timing of the regime transition under the VOC-rich condition is slower than that of the measured data, which could be attributed to overestimation of the NOx concentration. Both the measured and simulated timing of the regime transition estimated from the sensitivity to injection of O3 precursors NOx and VOC agree well with that estimated from the radical budget. The O3 production regimes estimated by the new instrument and by simulations are consistent with each other, suggesting that both methods are useful for estimating O3 production regime.