Date of Award
Ph.D. in Chemistry
This research focuses on studies of atmospheric mercury (Hg) using passive air samplers (PAS) and studies of trace elements in tree cores and sediment using inductively coupled plasma mass spectrometry (ICP-MS). Mercury is a toxic element that is dispersed globally through the atmosphere. Accurately measuring airborne Hg concentrations aids understanding of the pollutant’s sources, distribution, cycling, and trends. Mercury PAS are designed to capture gaseous elemental mercury (GEM) at a known rate. Compared to active air sampling the low-cost of PAS allows for greater spatial coverage. We used a commercially available Hg PAS (MerPAS®) and observed differences in GEM between landscapes, seasons, and elevations. Nearest to the surface, GEM levels were lowest in the wetland, where there was dense vegetation, and highest in an open grass field. GEM levels increased with the height above ground, except for the forest. We conclude that the PAS are capable of measuring GEM gradients between landscapes, elevations, and seasons, if given sufficient collection time, good analytical precision, and low blank levels. We also deployed the PAS along the northern Gulf of Mexico. We observed higher GEM levels (p < 0.05) in the winter compared to other seasons at all sites; with the general pattern being: winter > spring > summer > fall. Mean GEM levels were highest at Bay St. Louis, the western-most site nearest the New Orleans metropolitan area, and lowest at Cedar Point, a coastal marsh with extensive vegetation that can uptake GEM. Both the passive and active sampling methods showed the same seasonal trends and the difference between them was <15%, acceptable for evaluating larger spatial and temporal trends. Overall, we demonstrate that PASs can provide insight into GEM levels and the factors affecting them along coastal regions.
In a separate study, we developed an analytical method to measure trace metals, including Hg, in tree rings. Trees can incorporate certain pollutants into wood providing a historical pattern of deposition. We determined Hg in tree bole wood using a direct mercury analyzer (DMA), and then analyzed the ash for metals left behind after combustion using ICP-MS. The ash was digested using nitric and hydrofluoric acids. The method was optimized and validated, and then applied to trees in the Tallahatchie Experimental Forest in the Holly Spring National Forest to examine differences between species and to obtain background data for future studies of pollution point sources such as coal-fired power plants.
We also determined the historical deposition of metals in a marine sapropel from Mangrove Lake, Bermuda. Sapropel is an organic-rich sediment formed under conditions that can result in trace metal enrichment. We determined the concentration of total-mercury (Hg) and 17 other trace metals (Al, Ba, Ca, Cd, Cr, Cs, Cu, Fe, Li, Mn, Ni, Pb, Sr, Tl, U, V, Zn) in a sapropel core that dated back nearly two millennia. We established historical patterns of metal deposition on this remote island in the middle of the Atlantic Ocean, and use isotope ratios to assess possible pollution sources.
Jeon, Byunggwon, "APPLICATION OF PASSIVE AIR SAMPLERS FOR ATMOSPHERIC RESEARCH, AND DETERMINATION OF METALS IN TREE RINGS AND MARINE SAPROPEL BY ICP-MS" (2021). Electronic Theses and Dissertations. 2107.