Date of Award
Open Access Dissertation
Doctor of Philosophy in Atmospheric Sciences (PhD)
Administrative Home Department
Department of Physics
Committee Member 1
Committee Member 2
Committee Member 3
Committee Member 4
Aerosols are particles suspended in the atmosphere; they are emitted during natural phenomena such as dust storms, wildfires, and volcanic eruptions, and during anthropogenic activities like household wood burning, vehicles operations, and industrial productions, or they can form in the atmosphere from gas to particle partition. Aerosols impact earth’s weather and climate by absorbing and scattering the incoming solar and the outgoing earth thermal radiation and interacting with clouds. The optical properties of aerosols evolve as the chemical and physical properties vary during their residence in the atmosphere. In addition, the aerosols’ properties strongly depend on the vertical distribution in the atmosphere. Due to the dynamic and heterogenous nature of the aerosol properties, their optical characteristics are still highly uncertain and hence, it is essential to quantify their ability to absorb and scatter light. To address this knowledge gap, we studied atmospheric particles in three different regions of the world with different environmental conditions and particle compositions.
To investigate the details of aerosols as a function of height, we studied how their optical properties vary vertically using a tethered balloon system at the U.S. Department of Energy Atmospheric Radiation Measurement Southern Great Plains site in Oklahoma. We also estimated the top of the atmosphere radiative forcing using Lorentz-Mie simulations and the Santa Barbara Disort Atmospheric Radiative Transfer (SBDART) model. In a second study, we collected aerosol samples at a mountaintop site in Italy to study aerosols transported over long ranges. In the samples, we found an abundance of tar balls which are a kind of particles often detected in biomass-burning plumes (e.g., wildfire smoke). Tar balls absorb light at shorter wavelengths falling within the particle category often referred to as brown carbon; however, the reported complex refractive indices in the literature are highly variable. Therefore, we estimated the refractive index (RI) and optical properties of single tar balls using electron energy loss spectroscopy. We also estimated their radiative forcing to understand their potential impacts on climate and weather systems. In a third study on aerosol processing in haze conditions, we used microscopy and mass spectrometry techniques to observe the abundance of organosulfates formed through multiphase chemical reactions between organic and sulfate particles collected in the Indo-Gangetic region. The formation of organosulfates was recently shown to increase the light absorption by organic particles in the ultraviolet and visible spectral range. Finally, we classified aerosols based on their chemical composition and phase state which also affect the aerosol optical properties in complex manners.
My thesis discusses the chemical, physical, and optical properties of atmospheric aerosols providing data that can be used in climate and weather models to reduce uncertainties and enhance their predictability skills.
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Mathai, Susan, "PHYSICAL, OPTICAL, AND CHEMICAL PROPERTIES OF LIGHT ABSORBING AEROSOLS AND THEIR CLIMATIC IMPACTS", Open Access Dissertation, Michigan Technological University, 2023.