Research
Current Projects
Origin and Influence of Background Ozone in the Western U.S. from Observations at the Mount Bachelor Observatory
Ozone is a secondary pollutant produced in both the background atmosphere and urban/industrial environments. Wildfire smoke enhances ozone concentrations in populated areas, threatening human and environmental health. However the behavior of ozone in the smoke itself is more variable. In collaboration with the University of Washington, we are investigating the causes of variability in background ozone and in smoke-impacted air masses using long-term measurements from the high-elevation Mount Bachelor Observatory (MBO) in Central Oregon. We seek to better understand the factors that control ozone in isolated smoke plumes, and the relationship between ozone in the background atmosphere and at downwind surface sites.
Analytical Determination of the Emerging Tire-Wear Contaminant 6ppd-q in Stormwater Runoff
In 2021, 6ppd-q was identified as the contaminant responsible for urban runoff mortality syndrome, wherein large numbers of coho salmon were observed to die off near roadways following large rainfall events. A growing body of research has emerged about the sources and impacts of 6ppd-q on other fish species and in aquatic systems around the Pacific Northwest. We have been verifying the 6ppd-q quantification method in the ÈËÆÞÓÕ»ó Chemistry laboratory and are applying it to water and soil samples taken near our campus, such as in stormwater runoff to the ÈËÆÞÓÕ»ó Canyon or to other areas in the Johnson Creek watershed.
Use of the Dithiothreitol (DTT) Assay for Measuring the Oxidative Potential of Wildfire-Emitted Particulate Matter
Wildfire smoke, especially the particulate matter it contains, is linked with a variety of health effects and inflammatory responses in the human body. Oxidative Potential indicates the likelihood that inhaled particulate matter will deplete antioxidants and produce reactive oxygen species in the body, which can lead to these myriad health effects. We are interested in determining the oxidative potential of particulate matter in wildfire smoke. We are verifying published methods for a dithiothreitol (DTT) assay in our laboratory, and applying it to filter samples collected on clean air and smoke-impacted days on the ÈËÆÞÓÕ»ó campus. We hope to apply this sampling and analytical method to other sites in the future.
Mercury Oxidation in a Continental Atmosphere: High Temporal Resolution Measurements of Mercury and Oxidants at Storm Peak Laboratory
In 2021 and 2022, in collaboration with researchers at Utah State University, the University of Utah, and the University of Colorado-Boulder, we deployed a novel measurement system for elemental and oxidized mercury at the Storm Peak Laboratory (SPL) in Steamboat Springs, CO. We have since reported on the origins, underlying chemistry, and analytical advances in atmospheric mercury measured within the background mountaintop environment. Presently, we are analyzing the enhancements of both elemental and oxidized mercury detected in wildfire smoke plumes during the study, and drawing comparisons with the origins and transport pathways for different smoke events.
Published Work
(manuscripts from the past three years, 2023-2026)
*Current or former undergraduate student mentee
Elgiar, T.R.; Gratz, L.E.; Hallar, A.G.; Volkamer, R.; Lyman, S.N. Underestimation of atmospheric oxidized mercury at a mountaintop site by the GEOS-Chem chemical transport model. Atmos. Chem. Phys. 2025, 16387-16399. []
Hallar, A.G.; McCubbin, I.B.; Borys, R.; Lowenthal, D.; Wetzel, M.; Hindman, W.; Brooks, S.; Steenburgh, J.; Gratz, L.; Hoch, S.; Stephens, B.; Horel, J.; Molotch, N.; Mace, G.; Bailey, A.; Pettersen, C.; Andrews, E.; Czizco, D.; Garcia, M. Storm Peak Laboratory: A Research and Training Facility for the Atmospheric Sciences. Bull. Am. Met. Soc. 2025, 106(6), 10.1175/BAMS-D-24-0043.1. []
Weiss-Penzias, P.S.; Lyman, S.N.; Elgiar, T.; Gratz, L.E.; Luke, W.T.; Quevedo, G.; Choma, N.; Gustin, M.S. The effect of precipitation on gaseous oxidized and elemental mercury concentrations as quantified by two types of atmospheric mercury measurement systems. Env. Sci: Atmos. 2025, 10.1039/d4ea00145a. []
Lee, C.F.; Elgiar, T.; David, L.; Wilmot, T.Y.; Reza, M.; Hirshorn, N.S.*; McCubbin, I.; Shah, V.; Lin, J.C.; Lyman, S.N.; Hallar, A.G.; Gratz, L.E.; Volkamer, R. Elevated Tropospheric Iodine over the Central Continental United States: Is Iodine a Major Oxidant of Atmospheric Mercury? Geophys. Res. Lett. 2024, 51(17), e2024GL109247. []
Derry, E.J.*; Elgiar, T.R.; Wimot, T.Y.; Hoch, N.*; Hirshorn, N.S.*; Weiss-Penzias, P.; Lee, C.F.; Lin, J.C.; Hallar, A.G.; Volkamer, R.; Lyman, S.N.; Gratz, L.E. Elevated oxidized mercury in the free troposphere: Analytical advances and application at a remote continental mountaintop site. Atmos. Chem. Phys. 2024, 24, 9615-9643. []
Gustin, M.; Dunham-Cheatham, S.; Lyman, S.; Horvat, M.; Gay, D.A.; Gacnik, J.; Gratz, L.; Kempkes, G.; Khalizov, A.; Lin, C-J.; Lindberg, S.; Lown, L.; Martin, L.; Mason, R.; MacSween, K.; Nair, S.; Nguyen, L.S.P.; O’Neil, T.; Sommar, J.; Weiss-Penzias, P.; Zhang, L.; Zivkovic, I. Measurement of Atmospheric Mercury: Current Limitations and Suggestions for Paths Forward. Environ. Sci. Tech., 2024, 58, 12853-12864. []
Elgiar, T.R.; Lyman, S.N.; Andron, T.D.; Gratz, L.E.; Hallar, A.G.; Horvat, M.; Nair, S.V.; O’Neil, T.; Volkamer, R.; Zovdovic, I. Traceable Calibration of Atmospheric Oxidized Mercury Measurements. Environ. Sci. Tech. 2024, 58, 10706-10716. []
Lynam, M.M.; Oriol, L.; Mann, T.; Dvonch, J.T.; Barres, J.A.; Gratz, L.E.; White, E.M.; Landis, M.S.; Mahowald, N.; Xi, C.; Steiner, A.L. Atmospheric dry and wet deposition of total phosphorus to the Great Lakes. Atmos. Environ., 2023, 313, 120049. []