Ozone chemistry in western U.S. wildfire plumes.

Wildfires are a substantial but poorly quantified source of tropospheric ozone (O). Here, to investigate the highly variable O chemistry in wildfire plumes, we exploit the in situ chemical characterization of western wildfires during the FIREX-AQ flight campaign and show that O 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 chemistry exhibits rapid transition in chemical regimes. Within a few daylight hours, the O formation substantially slows and is largely limited by the abundance of nitrogen oxides (NO). This finding supports previous observations that O formation is enhanced when VOC-rich wildfire smoke mixes into NO-rich urban plumes, thereby deteriorating urban air quality. Last, we relate O 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.