The atmospheric aerosol burden affects air quality and climate, and is characterized with a variety of techniques, including optical and filter-based mass measurements. Aerosol optical properties are largely a function of particle size, which is influenced by chemical composition. Notably, aerosol composition that affects hygroscopicity plays a determining role in particle size by affecting water uptake. Aerosol liquid water (ALW) is an important and ubiquitous particle constituent. However, it is poorly characterized by regulatory surface monitoring networks that measure fine particulate matter (PM2.5) mass. Satellite measurements of aerosol optical depth (AOD) observe aerosols in situ with ALW intact. Surface measurements of PM2.5 mass concentrations are often compared to satellite AOD. This work seeks to reconcile filter-based mass and optical measurements of ambient aerosols through fundamental chemistry. I apply a thermodynamic model to ambient meteorological and particle chemical composition data across the contiguous United States (CONUS) to estimate ALW mass. I perform statistical analyses to establish significant associations among ALW and optical aerosol measurement techniques. The topics of air quality and climate often create an interested but sometimes misinformed public. Scientific literacy begins in the classroom by instructing students in fundamental science and chemistry so they can later apply these concepts in their chosen careers.
My dissertation aims to 1) reconcile ambient aerosol measurements made via different mass and optical techniques and platforms through understanding aerosol chemical properties and 2) improve student learning of contextualized analytical chemistry concepts via the development of interactive virtual prelab activities for an instrumental analysis course. To address these aims I 1) investigate the differences in aerosol physicochemical properties on cloudy and clear sky days at a surface monitoring location in the Midwestern U.S. from 2010 to 2019 (945,796 samples), 2) analyze decadal trends in the PM2.5-to-AOD ratio (eta) across the U.S. as a function of chemical composition from 2006 to 2015 (5,193,448 samples), and 3) assess changes in student learning outcomes and laboratory preparation after the addition of choose-your-own-adventure (CYOA) virtual prelab activities in an upper-division instrumental analysis chemistry course. In Bondville, Illinois, I apply cloud-screening quality assurance information in the AERosol RObotic NETwork (AERONET) data record in seasonal comparison of aerosol optical and physical properties on cloudy and clear sky days. With optical measurements, I find that ambient aerosols are physically larger on cloudy days and that ALW estimated from chemically speciated PM2.5 mass measurements is a plausible contributing explanation. Through surface observations of AOD and PM2.5, I calculate eta at multiple locations across the CONUS and assess chemical and optical properties over time. I compare surface observations of eta in August 2015 and January 2016 to Community Multiscale Air Quality (CMAQ) model simulations. I find the spatial and temporal variation in $\eta$ across humid and arid locations is influenced by chemical constituents that affect ALW mass concentrations, particularly on peak days. Comparison with two representative month-long CMAQ simulations for summer and winter reproduce similar spatial and temporal variability in eta to surface observations. I statistically compare laboratory report rubric learning outcomes between quarters with and without virtual prelab activities and conduct Likert opinion surveys across three offerings of an analytical chemistry laboratory class. I find that the addition of CYOA prelab activities improve student mastery of analytical chemistry concepts in laboratory reports and lessened student concerns about preparing for complex laboratory experiments. Future directions of this research include the need for quantitative understanding of ambient ALW and varied cloud-cover conditions, along with better preparing students via improving scientific literacy and contextualizing learning in the classroom to apply fundamentals in environmental chemistry measurements and analyses.
