Date of Award
10-21-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Mineral dust is a major component of ambient particulate matter (PM) globally, affecting visibility, air quality, human health, climate, and biogeochemistry. Dust mass cannot be directly measured and therefore is typically estimated using a dust equation to sum common oxides of major crustal elements based on measured elemental composition data. Both an accurate dust equation and reliable elemental data are essential to accurately estimate dust mass. However, most dust equations fail to account for all major dust compounds, exclude non-dust components of some elements, or account for regional variations in dust composition. Attenuation effects for light elements measured by the widely used X-ray fluorescence (XRF) technique can lead to underestimation of dust mass, yet correcting these effects in PM filter samples remains a significant challenge. Elemental characterization of PM also provides concentrations of trace elements, which can be strongly associated with morbidity and mortality. Ground-based monitoring of atmospheric elements is important to estimate the exposure to dust and trace elements, assess health risks, and investigate emission sources. However, many developing countries lack sufficient ground-based measurements of PM chemical composition. Uniform sampling protocols and reliable analyses are also needed to enable global comparisons. This dissertation includes four studies aimed at improving measurements and understanding of mineral dust and trace elements in ambient PM. In the first study, a global-scale mineral dust equation with region-specific coefficients was developed and evaluated for various types of dust from different regions. The global equation reduced regional biases by about 6-10% for desert dust in source regions compared to an existing equation (IMPROVE) that was designed for the U.S. The second study presented the methodology and implications for the elemental characterization of ambient PM for a globally distributed monitoring network, the Surface PARTiculate mAtter Network (SPARTAN). Consistent protocols were applied to collect PM samples and analyze them at one central laboratory. Health risk assessment indicated significant airborne arsenic pollution at sites in South and Southeast Asia. The third study focused on characterizing dust contribution to PM in Central Asia, an understudied dust source region, using the first contemporary elemental composition data of PM samples collected from Tashkent, Uzbekistan. Large dust events originating from different deserts were identified by time series analysis, backward trajectory analysis, and satellite images. The fourth study assessed attenuation due to mass loading and particle size for light elements by comparing XRF and gravimetric measurements of samples with known compositions. Theoretical attenuation models were compared with measurements and applied to ambient PM samples to assess their impact on dust concentration estimates. These studies collectively advance the understanding of airborne mineral dust and trace elements and inform global air quality management.
Language
English (en)
Chair
Randall Martin
Committee Members
Jay Turner; Jenny Hand; Jian Wang; Rajan Chakrabarty; Randall Martin