Investigation into the mechanisms of size-resolved particle dry deposition across three environments

Boedicker, Erin Kathleen, author
Farmer, Delphine, advisor
Ravishankara, A. R. Ravi, committee member
Volckens, John, committee member
Willis, Megan, committee member
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Airborne particulate matter, or aerosols, have significant impacts on radiative forcing through both their direct - scattering and absorbing light - and indirect effects- acting as cloud condensation nuclei and altering the lifetime of clouds. The magnitude of these effects is largely determined by particle lifetime, which is defined by their rate of removal through wet and dry deposition. Dry deposition, specifically of accumulation mode aerosols (0.1 – 1 µ), is one of the largest sources of uncertainty in global models. The processes that influence deposition are poorly constrained and few comprehensive measurements are available to improve our understanding. Characterizing these mechanisms is vital for predicting spatial and temporal trends in particle dry deposition and lifetime. While there have been improvements in quantifying and understanding dry deposition, large gaps in our knowledge still exist that make predicting the impacts of aerosols on Earth's climate difficult. To improve understanding of the underlying mechanisms that determine the rate of particle deposition in an environment this dissertation reports size-resolved dry deposition measurements from three distinct environment types. First, we report measurements from a test house which identify dilution and deposition as the most important factors influencing particle concentrations indoors. This analysis also shows that deposition indoor is governed by the same fundamental process that we consider for outdoor environments. Second, we present particle flux and deposition measurements from a Ponderosa pine forest over four seasons where significant enhancement in deposition during the wintertime was observed. This is attributable to changes in interception, caused by changes in plant physiology and surface structure during the winter that leads to an increase in their ability to uptake particles. Finally, we show particle and black carbon deposition from a low Arctic tundra during snow-cover that are elevated compared to predictions of dry deposition in that region. Incorporating interception into the model parameterizations improved model measurement agreement and provides evidence to suggest that surface structure and microroughness impact deposition even when there is snow-cover.
2022 Summer.
Includes bibliographical references.
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