My main interest is ozone in the part of the atmosphere closest to the earth (the troposphere) and the role it plays in determining atmospheric chemistry, vegetation and climate connections. Ozone in the troposphere is an air pollutant, injurious to human health and vegetation, and a potent greenhouse gas. Tropospheric ozone also controls the atmospheric oxidative capacity, meaning that it 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 by the earth’s surface. We call this sink ozone dry deposition. Understanding spatial and temporal variability in ozone dry deposition is key to modeling the tropospheric ozone budget 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 (for photosynthesis!) and ozone and release water vapor into the atmosphere. This ozone plant injury can impact regional-to-global carbon and water cycles and ozone pollution.
Ozone dry deposition also occurs via other (“nonstomatal”) pathways. Nonstomatal uptake pathways are poorly understood despite recent research (including our own!) suggesting that nonstomatal deposition can be a substantial amount of the total, varying strongly in space and time.
I investigate spatiotemporal variability in ozone dry deposition using a variety of ground-based measurements and a hierarchy of models from process-level models to global chemistry-climate ones. We published a paper in GRL in 2017 on the strong observed year-to-year differences in ozone deposition velocity (the velocity tells us about the strength of ozone removal at the surface, but is independent of ambient ozone concentrations) at Harvard Forest (a deciduous forest and long-term ecological monitoring site in central Massachusetts). Harvard Forest has one of the longest existing datasets of ozone dry deposition measurements (11 years) with coincident meteorological and biophysical observations. We found that this strong interannual variability at Harvard Forest is driven by nonstomatal uptake. However, it’s unclear what the meteorological or biophysical drivers of these year-to-year differences are. 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.
For more information on ozone dry deposition, this is a lecture that I gave to Columbia University students in Arlene Fiore’s Intro to Atmospheric Chemistry class.