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

The sensitivity of tropospheric ozone (O) to its precursors volatile organic compounds (VOCs) and nitrogen oxides (NO) determines the emission reduction strategy for O mitigation. Due to the lack of comprehensive vertical measurements of VOCs, the vertical distribution of O sensitivity regimes has not been well understood. O precursor sensitivity determined by ground-level measurements has been generally used to guide O control strategy. Here, to precisely diagnose O 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 and other relevant parameters. Our results suggest that the O precursor sensitivity shifts from a VOC-limited regime at the ground to a NO-limited regime at upper layers, indicating that the ground-level O 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 O precursor sensitivity is in urgent need for the development of effective O control strategies.