Research – Atmospheric Chemistry at Colorado College

My research can be broadly divided into the following three themes:

Mercury (Hg) atmospheric chemistry and biogeochemical cycling,
Long-range transport of atmospheric pollutants, and
Impacts of urban/industrial emissions on local and regional air quality.

I use both long-term and intensive field measurements to quantify the levels of pollutants in ambient air and atmospheric deposition. I then apply meteorological and statistical models to explain the atmospheric chemistry and transport of emitted species. My research therefore balances laboratory method development, field measurements, and data analyses. Below are my areas of active research at Colorado College.

Mercury oxidation pathways in a continental atmosphere: High temporal resolution measurements of mercury and oxidants at Storm Peak Laboratory

Oxidized mercury is the most reactive, water soluble, and bioavailable form of mercury in the atmosphere. Identifying atmospheric oxidation pathways is paramount to fully understanding mercury cycling and fate. Reactive bromine has been proposed as the globally-dominant mercury oxidant and was shown to dominate in coastal and marine environments, but its role in the continental boundary layer and/or free troposphere remains less clear. Recent modeling studies suggest mercury oxidation chemistry may involve multiple pathways under different atmospheric conditions. We have developed a dual-channel mercury analyzer and an automated oxidized mercury calibrator that do not suffer from the known low bias of commercial instrumentation. We deployed this instrument in a preliminary study in the Colorado Front Range in Summer 2018. We now plan further develop and deploy these instruments and a MAX-DOAS for detecting halogens and other reactive gases alongside a suite of chemical and meteorological in-situ instruments for long-term observations at the high-elevation Storm Peak Laboratory (SPL) in Steamboat Springs, Colorado, USA. We will conduct air trajectory and photochemical modeling to determine the origins of sampled air masses and investigate the chemical mechanisms responsible for observed mercury speciation in a continental atmosphere. Our multi-year, multi-season study will address major areas of uncertainty in atmospheric mercury chemistry, namely the characterization of the governing oxidation mechanism(s) in a remote continental atmosphere.

NSF Award number 1951515; Collaborative project with Dr. Seth Lyman (Utah State University), Prof. Gannet Hallar (University of Utah) and Prof. Rainer Volkamer (University of Colorado).

Preliminary work: Funding provided by the Colorado College Natural Sciences Division, Dean’s SEGway Program, Southwest Studies Program Jackson Fellowship, SCoRe Program, and Grant Lyddon. Preliminary results were presented at the 2019 ICMGP and 2019 AGU Fall Meeting. A manuscript is under review for publication in Environmental Science and Technology. Colorado College undergraduate students Story Schwantes (’19) and Melissa Taing (’19) supported this work.

Sources and temporal variability of ambient mercury in Colorado Springs, CO

Colorado Springs is the second largest population center in Colorado. While there are relatively few Hg point sources in the city compared to some other U.S. urban areas, it is home to the centrally located Martin Drake CFPP, which provides a significant fraction of the electricity for the local community but has been the center of much scrutiny due to increasing concerns over the age of the plant, its impact on local air quality, and emissions of greenhouse gases. From June to October 2016 we continuously measured total gaseous Hg (TGM = gaseous elemental Hg (GEM) + gaseous oxidized Hg (GOM)), carbon dioxide (CO2), SO2, carbon monoxide (CO), and meteorological parameters at a CDPHE air quality monitoring site approximately one mile north-northwest of Martin Drake. We found that the current Hg emissions from the CFPP did not significantly influence local TGM, which is consistent with the facility’s relatively low reported annual emissions of 0.20 kg Hg per year. Instead, variability in the regional signal, diurnal meteorological conditions, and/or near-surface emission sources appears to more greatly influence TGM at this urban site.

This work was completed and published in April 2019 in a special issue on “Atmospheric Mercury: Sources, Sinks, and Transformations” for the open-access journal Atmosphere, and can be found here.

Funding provided by the Colorado College Natural Sciences Division and SCoRe Program. Colorado College undergraduate students Evan Laufman (’18) and Story Schwantes (’19) supported the work. Preliminary results presented at IGAC Science Conference 2016, AMS Annual Meeting 2017, and AMS Student Symposium 2019.

Spatial patterns in summertime surface ozone in the southern Front Range of the Rocky Mountains, USA

Summertime ozone in the western United States presents a unique regulatory challenge. In some cities within the region, steadily increasing background ozone and growing populations combined with complex topography and meteorological conditions may intensify ozone production and threaten compliance with the National Ambient Air Quality Standards. Colorado Springs, Colorado is one such example, wherein the annual mean 8-hour ozone concentration with exceptional events excluded, has increased by approximately 5 ppb in the past 15 years. While there is considerable research on surface ozone and its origins in the northern Front Range, particularly in the Denver-Julesburg basin, less is known about ozone distribution and production in the Pikes Peak region, which is located approximately 100 km south of Denver. From June through September 2018, the Colorado Department of Public Health and Environment measured hourly ozone concentrations at eight sites, the two permanent sites in operation since 2000 and 2004 and six temporary sites, to characterize the spatial distribution of ozone in the Pikes Peak region. In this project we look at the effects of atmospheric transport, topography, and exceptional events on ozone concentrations across Colorado Springs, and assess the representativeness of permanent monitoring stations in the area. Our results expand current knowledge of ozone in the Colorado Front Range and lay groundwork for managing ozone in a growing metropolitan area.

Funding provided in part by the Colorado College SCoRe program. Preliminary results presented at the 2019 AGU Fall Meeting and a manuscript is in preparation. Colorado College undergraduate student Margot Flynn (’20) supported the work.

Relationships between metal contamination, health, and plumage characteristics of songbirds in Southeast Michigan

Reproductive success is central to the persistence of wild animal populations. Animals use visual cues to communicate fitness and potential reproductive success to mates, but if those signals are disrupted due to environmental changes, such as metal pollution, there may be negative consequences on fitness and reduced reproductive success. Birds are exposed to metals through diet or by coming into physical contact with air, water, or land pollution, where the metals are then carried by the blood and incorporated in growing feathers. In this project, we seek to explore the potential disruptive relationships between human-caused environmental contamination and urban songbird populations. Specific research questions consider whether songbird plumage or blood plasma reflect local environmental pollution, and whether metal contaminants such as lead and mercury are reducing plumage mating signals. We seek to determine how metal pollution impacts urban wildlife through interactions with feather quality, specifically whether or not contaminated drinking water is increasing contaminant levels in wild animal tissues and if carotenoid-dependent plumage can serve as an effective biomonitoring tool.

Funding provided by the Colorado College Natural Sciences Division. Project developed in collaboration with Dr. Jamie Cornelius, Eastern Michigan University, and Dr. Brian Majestic, University of Denver. Abstract submitted for presentation at SETAC 2020. Colorado College undergraduate student Saria Sato Bajracharya (’20) is supporting this work.

Isotopic composition of background elemental mercury

The use of Hg isotopic ratios has emerged as a viable and innovative method to investigate Hg biogeochemical cycling. The type (mass dependent or mass independent) and extent of isotopic fractionation detected in environmental samples has been used to elucidate a wide range of emission sources and environmental process, including the transformation pathways of atmospheric Hg. Studies using Hg stable isotope analysis of precipitation and ambient air samples have found that both industrial and natural processes can alter the isotopic signature of atmospheric Hg. As a result, ambient air samples that are representative of the background global atmospheric GEM pool are hypothesized to have a distinctly different isotopic signature from those samples which contain industrially emitted or naturally processed Hg. However, thus far no study has isolated free tropospheric samples of global background air (i.e. air that has not been recently influenced by surface emissions) for Hg isotopic analysis. In summers 2016 and 2017 I collaborated with the research group of Professor Joel Blum (University of Michigan) to collect samples of ambient air and wet deposition at three high elevation measurement sites in the western U.S.: Storm Peak Laboratory (Steamboat Springs, CO), Mt Bachelor Observatory (Bend, OR), and Rendezvous Mountain (Jackson, WY). With continued method development and sampling, as well as the use of meteorological transport analysis, we aim to isolate the isotopic composition of background GEM as well as other sources that may contribute to free tropospheric Hg.

Funding provided by the Colorado College Dean’s SEGway fund and the Mrachek Fellowship. Preliminary analyses accepted for presentation at the Goldschmidt Conference, August 2019. Manuscript under review for publication in Environmental Science and Technology.

Hg retention and transport in terrestrial ecosystems following severe fire

Vegetation and soil are known reservoirs for atmospheric Hg uptake and sequestration. Vegetation takes up atmospheric Hg via both wet and dry deposition, wherein throughfall and litterfall transport Hg to the surface where it can be incorporated into the soil. Wildfire is a major ecosystem perturbation that releases stored Hg back to the atmosphere and also changes important ecosystem properties (i.e. canopy cover, soil structure and quality). Beyond the release of Hg to the atmosphere, severe fire may alter the ability of the soil to take up and retain Hg as the ecosystem recovers from the disturbance. This has implications for the fate and transport of atmospherically deposited Hg. In the western U.S., earlier and prolonged spring/summer conditions caused by climate change have led to increased wildfire activity and longer fire seasons in recent decades, potentially affecting Hg cycling in forest ecosystems. In summer 2016 we collected soil cores within the burn scars and nearby reference sites of three severe 2002 wildfires in Colorado that have experienced little forest regrowth more than a decade later. Cores were taken along hillslope gradients within each watershed and analyzed for Hg and carbon content. Our objective is to determine how severe fire (and the complete removal of forest canopy) affects (1) retention of Hg in the terrestrial ecosystem and (2) transport of Hg to the aquatic ecosystem where it can become methylated and pose a threat to ecosystem and ultimately human health.

Funding provided in part by the Colorado College Natural Sciences Division and Grant Lyddon. Preliminary results presented at ICMGP 2017.