Comparative ozone production sensitivity to NO_x and VOCs in Quito, Ecuador and Santiago, Chile: implications for control strategies in times of climate action

Abstract. Amid the current climate crisis, cities are being called to reduce levels of atmospheric pollutants that are short-lived climate forcers (SLCF) such as ozone and PM_2.5. This endeavor presents new challenges in terms of control strategies. Here, we scrutinize the ozone production sensitivity to NO_x and VOCs in Quito, Ecuador and Santiago, Chile, and we discuss the implications for precursor controls. To this end, we use a chemical box-model constrained with VOCs, meteorological, and air quality data. Comparable ozone production rates (P(O₃)=15–35 ppbv h^-1) were found to influence both cities, which lead to a well-established ozone season in Santiago, but not in Quito. A partial explanation to this difference is the distinct mixing conditions in both cities. Alkenes and aromatics contribute 60–90 % to ozone production in Quito and 50–60 % in Santiago. Aldehydes and ketones contribute an additional 20–30 % in Santiago. Isoprene contributes 10 % in Quito and 20 % in Santiago. Any isolated measure to reduce NO_x alone would impact both cities negatively. For example, a 75 % reduction in NO_x causes a 30 % increase in peak P(O₃) in Quito and a 54 % increase in Santiago. In contrast, equal reductions in NO_x and VOCs would have a beneficial effect. For example, a 75 % decrease in both precursors would cut the peak P(O₃) by more than half in both cities. Therefore, only parallel controls on NO_x and VOCs in both cities have the potential of curbing ozone from the simultaneous perspective of public health and climate action.