My research focuses on ozone in the part of the atmosphere closest to the earth (the troposphere) where it is an air pollutant and a potent greenhouse gas. Tropospheric ozone is also central to the atmospheric chemistry that determines how long other reactive greenhouse gases and air pollutants stay in the atmosphere. An important, yet overlooked and uncertain part of the tropospheric ozone budget is uptake of ozone by the earth’s surface, or dry deposition. Resolving trends and variability in dry deposition of ozone is important for modeling tropospheric ozone and air quality accurately.
Ozone dry deposition occurs when ozone diffuses into the small pores on plant leaves called stomata. These are the same pores that plants use for gas exchange of carbon dioxide and water vapor. Stomatal uptake of ozone is injurious to the plant and can change the plant’s ability to take up carbon dioxide and release water vapor into the atmosphere. Ozone dry deposition also occurs via other (“nonstomatal”) pathways. Nonstomatal deposition is poorly understood but has been shown to be a substantial amount of the total deposition.
I investigate spatiotemporal variability in ozone dry deposition using a variety of ground-based measurements and a model hierarchy. We published a paper in GRL in 2017 on the strong year-to-year differences in ozone dry deposition velocity at Harvard Forest, which has one of the longest observational datasets of ozone dry deposition. This strong interannual variability is not simulating by a leading chemistry transport model (GEOS-Chem), which suggests that using this model to interpret year-to-year differences in ozone concentrations may lead to an overemphasis of the role of emissions.
We found that the strong interannual variability in ozone dry deposition at Harvard Forest is primarily driven by nonstomatal deposition. However, the meteorological or biophysical drivers of this variability are unclear. I am working now to expand our analysis regionally and examine variability on shorter timescales in order to shed light on what these controls may be.