Insights into the Role of Meteorology on Improving Model-Measurement Agreement of Oxidants in Forested Environments

TitleInsights into the Role of Meteorology on Improving Model-Measurement Agreement of Oxidants in Forested Environments
Publication TypeThesis
Year of Publication2021
AuthorsKavassalis SC
Academic DepartmentGraduate Department of Chemistry
DegreeDoctor or Philosopy
UniversityUniversity of Toronto
Thesis TypeDissertation

Within forest canopies, biogenic emissions and anthropogenic pollutants interact through complex chemical reactions, impacting atmospheric composition, climate, and ecosystem processes. The need to understand the biosphere-atmosphere exchange of heat, momentum, and chemical species has led to a
significant body of work on the transport and fate of molecules within and above plant canopies. The
impact of these canopies on the fast oxidation chemistry responsible for regulating the lifetime of greenhouse gases is still insufficiently understood. This is largely owing to the complexity of the chemical
reactions involved and the lack of fully explicit physical descriptions of in-canopy turbulence and deposition. This thesis investigates the role that improved meteorological representation can play in reducing
model error for simulated chemistry and improving our understanding of oxidation chemistry in forested
I examine long-term air quality monitoring data to show evidence that ozone mixing ratios in much
of the United States are impacted by the presence of vegetation through the ability of plants to remove
ozone from the atmosphere, and that this dry deposition sink is regulated by vapor pressure deficit.
Examining the role of forest canopies in modulating chemistry further, I used the FORest Canopy Atmosphere Transfer (FORCAsT) model to simulate dynamics and reactions in a forest at the University
of Michigan Biological Station (UMBS). I found that updating modeled meteorology by assimilating
observations improves simulations of primary species, but key discrepancies in oxidation products exist,
suggesting possible changes to branching ratios in the chemical mechanism may be needed. I use the
micrometeorology measurements I made at the UMBS in conjunction with high resolution volatile organic compound (VOC) data to determine the impact of turbulence on VOCs, providing novel data for
future model validation and parameterization. Further, I simulate the impact of turbulence on chemical
reactions by incorporating the turbulence-induced covariance between chemical reactants in a box model
and show that turbulent fluctuations strongly impact reactions involving short-lived radicals, leading to
significant concentration changes, at canopy height. This work contributes to our understanding of the
impact that meteorology plays on oxidation chemistry in and above forests.

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