Ozone sensitivity regimes vary at different heights in the planetary boundary layer

The sensitivity of tropospheric ozone (O₃) to its precursors volatile organic compounds (VOCs) and nitrogen oxides (NO_X) determines the emission reduction strategy for O₃ mitigation. Due to the lack of comprehensive vertical measurements of VOCs, the vertical distribution of O₃ sensitivity regimes has not been well understood. O₃ precursor sensitivity determined by ground-level measurements has been generally used to guide O₃ control strategy. Here, to precisely diagnose O₃ sensitivity regimes at different heights in the planetary boundary layer (PBL), we developed a vertical measurement system based on an unmanned aerial vehicle platform to conduct comprehensive vertical measurements of VOCs, NO_X and other relevant parameters. Our results suggest that the O₃ precursor sensitivity shifts from a VOC-limited regime at the ground to a NO_X-limited regime at upper layers, indicating that the ground-level O₃ sensitivity cannot represent the situation of the whole PBL. We also found that the state-of-the-art photochemical model tends to underestimate oxygenated VOCs at upper layers, resulting in overestimation of the degree of VOCs-limited regime. Therefore, thorough vertical measurements of VOCs to accurately diagnose O₃ precursor sensitivity is in urgent need for the development of effective O₃ control strategies.