Date of Award

Summer 2022

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

Margaret E Greenslade

Second Advisor

John G Tsavalas

Third Advisor

Christopher F Bauer

Abstract

Aerosols impact our lives in many different ways, including the health of our species,visibility and the global climate. In terms of climate effects, large uncertainty still exists surrounding the combined influence of aerosols on the Earth’s radiative budget. This highlights the importance of research that seeks to better understand atmospheric aerosols and associated gas phase compounds, as advances in the field will allow for the production of more accurate climate models. In laboratory studies, great variability in reported deliquescence relative humidity (DRH) warrants the need for new methods of analysis. A custom built electrobalance with variable active particle humidity control (EVAP-HC) allows for the experimental correlation between droplet growth or evaporation and relative humidity. Using EVAP-HC the DRH for glutaric and malonic acid, species relevant to atmospheric aerosol, were determined to be 90.4 ± 0.3 and 80.2 ± 0.3, respectively. While there are a variety of experimental techniques that can be used to observe the hygroscopic nature of aerosol, cavity ring-down spectroscopy (CRDS) coupled with humidification allows for a comparison of light interactions under dry and humidified environmental conditions. Results indicate a statistically significant enhancement of fRHext by 47%, corresponding to a 14% difference in reported growth factors (GF), for malonic acid that was dried in the bulk phase prior to dry-generation compared with malonic acid that was dry- generated as is, directly from the storage bottle. This finding signifies the importance of sample preparation for aerosol studies utilizing dry-generation. Biomass burning is a primary emission source for a host of gas- and aerosol-phase compounds, which can damage environmental and human health. During the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign in July and August of 2019, reactive nitrogen species were measured (NOx, NO2, HONO, HNO3 & p-NO3-), in wildfire plumes aboard NASA Langley’s Mobile Aerosol Characterization Laboratory (MACH-2). Daytime far-field smoke contained statistically higher or equivalent HONO to PM2.5 (particles that have aerodynamic diameter less than 2.5 micrometers) ratios compared to near-field smoke from the same fires. In the largest fire sampled during the day, UV-A irradiation was highly correlated (R2 = 0.9) with HONO to nitrogen dioxide (NO2) ratios indicating that photoenhanced NO2 to HONO conversion, likely facilitated by ground surfaces (e.g. soil, foliage, and dust), more than compensated for rapid photolytic loss of HONO.

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