Ozone chemistry in western U.S. wildfire plumes

Wildfires are a substantial but poorly quantified source of tropospheric ozone (O(3)). Here, to investigate the highly variable O(3) chemistry in wildfire plumes, we exploit the in situ chemical characterization of western wildfires during the FIREX-AQ flight campaign and show that O(3) production can be predicted as a function of experimentally constrained OH exposure, volatile organic compound (VOC) reactivity, and the fate of peroxy radicals. The O(3) chemistry exhibits rapid transition in chemical regimes. Within a few daylight hours, the O(3) formation substantially slows and is largely limited by the abundance of nitrogen oxides (NO(x)). This finding supports previous observations that O(3) formation is enhanced when VOC-rich wildfire smoke mixes into NO(x)-rich urban plumes, thereby deteriorating urban air quality. Last, we relate O(3) chemistry to the underlying fire characteristics, enabling a more accurate representation of wildfire chemistry in atmospheric models that are used to study air quality and predict climate.