Constraints on ozone removal by land and implications for 21st Century ozone pollution

Ozone dry deposition, an important tropospheric ozone sink, is expected to evolve with climate and land use, but coarse representation of ozone dry deposition in most large-scale atmospheric chemistry models hinders understanding of the influence of this sink on ozone air quality. Ozone uptake by stomata, injurious to plants, has been emphasized in the atmospheric chemistry community as the predominant terrestrial ozone depositional sink. However, there is an abundance of observational evidence from monitoring sites around the world suggesting that nonstomatal deposition processes (e.g., surface-mediated aqueous reactions on leaf cuticles, reactions with soil organic matter) are important ozone sinks. With observations from one of the longest ozone eddy covariance datasets available and a model hierarchy, I find substantial variations in nonstomatal ozone dry deposition, which is a non-negligible amount of the total ozone dry deposition, and identify the individual deposition processes driving observed variability. I pinpoint the responses of ozone pollution to changes in precursor emissions, climate, and ozone dry deposition at the beginning and end of the 21st century using a new version of the NOAA GFDL chemistry-climate model that more explicitly resolves deposition processes by leveraging the interactive biophysics of the land component of the model. My work highlights that under strong precursor emission controls there is a shift in the high ozone pollution season over northern mid-latitudes to a wintertime peak, and that wintertime ozone is sensitive to ozone dry deposition due to the long ozone lifetime. For both summer and winter, I find that neglecting variations in nonstomatal deposition and dependencies on environmental conditions may hinder accurate identification of the processes driving observed trends and variability in ozone pollution. In light of the sensitivity of ozone to dry deposition during winter, I identify a need for developing observational constraints on the wintertime depositional sink.