New observational constraints on the temperature dependence of ozone production and loss

Barry, Laura, Environmental Sciences - Graduate School of Arts and Sciences, University of Virginia
Pusede, Sally, AS-Environmental Sciences (ENVS), University of Virginia

Ozone (O3) air pollution is sensitive to climate change. O3 is a secondary pollutant, and its abundance and impacts are controlled by production and loss processes, both of which vary with temperature. Controls on O3 precursors, especially nitrogen oxides (NOx ≡ NO + NO2), are potentially an effective O3-related climate adaptation strategy when and where O3 variability is driven by O3 production (PO3) chemistry. In locations where O3 loss (LO3) controls O3 concentrations, the response of O3 dry deposition to climate change will determine future O3 concentrations. In this dissertation, I provide new insight into the temperature dependence of PO3 and LO3 and discuss the implications of these relationships for O3 variability in a changing climate. In Chapter 2, I present O3-temperature relationships in 1999–2001 and 2017–2019 on weekdays and weekends in climate regions and cities across the contiguous U.S. and explore their trends with NO2. In Chapter 3, I present eddy covariance measurements of O3 flux (FO3) and deposition (vd) velocity in a Central Virginia forest. In Chapter 4, I present stomatal and nonstomatal O3 deposition velocity relationships with temperature. I show that since 1999–2001, O3 climate penalties (mO3-T), defined as the slope of the O3-temperature correlation, decreased and weakened in most, but not all, climate regions (by 0.4–1.2 ppb ºC–1 when decreases occurred) and in many urban areas (by 0.2–2.1 ppb ºC–1 when decreases occurred). I demonstrate that when mO3-T are driven by PO3, they are responsive to NOx emissions reductions under higher NO2 conditions than O3 mixing ratios. Additional NOx controls will further lower mO3-T in many major cities with O3 nonattainment designations, even where PO3 chemistry continues to be NOx suppressed. I discuss the instrumentation, calibrations, and spectral and uncertainty analyses required to measure FO3 and O3 vd on a forest research tower. I measure the highest O3 mixing ratios in Central Virginia in the spring and the highest O3 vd in the summer, with half-hourly O3 vd frequently ranging from 1–1.5 cm s–1. I show that inverse relationships between daytime stomatal conductance and temperature on hot days (≥32ºC) suppress O3 vd and increases the O3 mixing ratios and that on warm nights (≥24ºC), an increase LO3 to within-canopy chemistry lowers O3 mixing ratios, offsetting daytime increases. This work can inform O3 pollution reduction and climate adaptation strategies in polluted urban areas and provides a modeling constraint for LO3 in the Southeast U.S.

PHD (Doctor of Philosophy)
air pollution, ozone, ozone deposition, ozone climate penalty
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