23STUDENT Establishing a Satellite-Derived Measure to Assess the Sensitivity of O3-NOx-VOC for Global Urban Areas

Ozone (O₃) near the surface is one of the criteria air pollutants, and it has adverse effects on public health and the environment. O₃ is formed through the photochemical reactions between its precursors NO_X and VOCs. Satellite instruments have provided continuous global observations of O₃ precursors, namely NO₂ and formaldehyde (HCHO, a proxy for VOCs), for nearly three decades. Here we aim to use satellite observations of NO₂ and HCHO to evaluate the O₃ production regimes over 96 global cities belonging to C40, a global network of cities with a shared commitment to confront the climate crisis. Simulations from a publicly available, global, high-resolution model (NASA’s GEOS-CF) are used to build the relationship between O₃ production regimes and column-based HCHO/NO₂, and also to identify the threshold values separating the NO_x-limited versus VOC-limited regimes. We find that the threshold values vary across cities and by season. We then apply the spatiotemporally varying threshold values to satellite observations of NO₂ and HCHO columns retrieved from OMI and TROPOMI, from which we identify the O₃ production regimes over urban areas and their spatial and temporal variations. Our results provide insights into the O₃ production regimes over global cities, including regions with sparse monitors, which could guide emission control strategies.