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SPL Research

An in situ Closure Study of Mixed Phase Clouds

PIs: Dan Cziczo, Purdue University, and Gannet Hallar, University of Utah

Clouds are commonly differentiated by the precipitation that reaches the surface, either rain or snow. This means they are often thought of as being liquid water, also called warm clouds, or ice, also called cold clouds. Those clouds that contain liquid water droplets and ice crystals at the same time are called mixed phase clouds. Mixed phase clouds are currently poorly understood because of the complicated mixture. Our lack of understanding of clouds, particularly those that are mixed in phase, limits our ability to understand precipitation, the atmosphere chemistry and climate. This project will determine the particles on which the droplets and ice crystals in mixed phase clouds form by deploying a new inlet and both warm and cold cloud chambers at Storm Peak Laboratory. Storm Peak is a high altitude site located in the Rocky Mountains in north-central Colorado that is among only a handful of sites worldwide that offers scientific laboratories where mixed phase clouds exist for long time periods. Using this new inlet, the research team will carry out two-season long observational studies of droplet and ice crystals within mixed phase clouds. This project will allow a resolution of the question of which atmospheric particles make droplets, which make ice crystals, and which do not effectively make either.

Mercury Oxidation Pathways in a Continental Atmosphere: High Temporal Resolution Measurements of Mercury and Oxidants

PIs:  Lynne Gratz, Colorado College; Seth Lyman, Utah State University; Rainer Volkamer, University of Colorado; Gannet Hallar, University of Utah

This project focuses on the study of atmospheric mercury. Mercury in the atmosphere exists in the gas-phase elemental form, as gas-phase oxidized mercury compounds, and bound to particles. The primary effort of this research will be on processes and mechanisms that govern oxidation reactions in the remote continental atmosphere. Mercury is a toxin that impacts neurological health and development in humans. A more thorough understanding of the atmospheric concentrations and chemical pathways of oxidized mercury is central to fully determining its fate. 

There are three objectives to this project: (1) Generate a high-quality dataset with accurate concentrations of elemental and oxidized mercury, halogen oxide radicals, aerosol size distribution, and other oxidants at a remote mountaintop site over the continental U.S.; (2) Identify the chemical mechanisms and physical processes that influence elemental and oxidized mercury in the free troposphere and the planetary boundary layer air masses; and (3) Bolster existing long-term measurements at Storm Peak Laboratory (e.g., to inform sources of new particle formation) and facilitate dialogue with researchers at other mountain observatories by sharing data analysis tools and expertise on best practices for sampling oxidized mercury, nanoparticles, and halogens from high elevation ground-based platforms.


The U.S. Department of Energy  deployed the second ARM Mobile Facility (AMF2) to Steamboat Springs, Colorado, in 2010-2011 for the Storm Peak Lab Cloud Property Validation Experiment (StormVEx). The already extensive instrument suite at SPL was augmented with additional state of the art instruments that are typically used for airborne cloud research.  SPL collected in situ cloud and precipitation property measurements while the AMF2 operated at a location approximately 2.4 km west and 500 m in elevation.  SPL researchers were funded by the U.S. Department of Energy Atmospheric Science Research Program in 2015 to continue working with the data collected during StormVEx. 


Inhibition of Snowfall by Pollution Aerosols (ISPA) is an ongoing project supported by the National Science Foundation since 2001. This study investigates the relationships among pollution aerosols, snow growth by riming, and snowfall amounts on the ground. ISPA results have important implications for water resources in the inter-mountain West. The principal investigator is Doug Lowenthal of DRI.

Hygroscopic Growth of Organic Aerosols

Aerosols contribute to the Earth’s radiation balance directly by absorbing and scattering light and indirectly by nucleating cloud droplets which increase planetary albedo. Both effects depend on hygroscopic growth, but the contribution of organics to aerosol hygroscopicity is not well understood— limiting efforts to model those effects. The study addresses several important questions through field measurements, laboratory experiments, and modeling. This project is a collaboration with Drs. Hallar, Lowenthal, Zielinska, and Chow at DRI; Dr. Mazzoleni at Michigan Technolgical University; Dr. Collins at Texas A&M, and Dr. Clegg at University of California, Davis. Aerosol filter samples were collected at Storm Peak Laboratory for future analysis.


Storm Peak Lab


SPL Research



SPL Education and Outreach



Gannet Hallar, Ph.D.
Lab Director



P.O. Box 882530
Steamboat Springs, CO 80488


Last Updated: 2/16/22