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

ABSTRACT

The sensitivity of tropospheric ozone (O3) to its precursors volatile organic compounds (VOCs) and nitrogen oxides (NOX) 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, NOX and other relevant parameters. Our results suggest that the O3 precursor sensitivity shifts from a VOC-limited regime at the ground to a NOX-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.