Observing the diurnal cycle of ozone-NOx-VOC sensitivity from geostationary satellite retrievals of ozone precursors

Ozone (O₃) near the ground is an air pollutant harmful to human health and ecosystems. O₃ production is nonlinearly dependent on the availability of its precursors: NO_x and VOCs. A major challenge in mitigating urban O₃ pollution is to determine whether the O₃ production is NO_x-limited or VOC-limited. Satellite-observed ratio of formaldehyde (HCHO) to NO₂ reflects the relative availability of reactivity-weighted VOCs and NO_x, which has been applied to sun synchronous satellite observations to diagnose O₃-NO_x-VOC sensitivity in the early afternoon. Here we present our recent work on using new geostationary satellite observations to diagnose the diurnal variations of O₃-NO_x-VOCsensitivity. We couple a global chemical transport model with a steady-state model to derive the regime threshold value separating NO_x-limited and VOC-limited regimes. We evaluate how the diurnal variations of column-to-surface relationship, HCHO production from VOCs, and the oxidative capacity affect the regime threshold values. Next, we apply the derived regime threshold to TEMPO and GEMS geostationary satellite observations of NO₂ and HCHO, from which we identify the hourly variations of O₃ production regimes over the North America and East Asia.