Laboratory and Surface-based Studies of Atmospherically-relevant Ice Nucleating Particle Sources, Concentrations and Compositions

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The formation of ice on atmospheric particles is a basic process that can impact climate through both the hydrological cycle, via influencing the efficiency and distribution of precipitation, and through impacts on the scattering of solar and thermal radiation by ice-containing clouds. Incomplete understanding of the role of changing natural and human-influenced particle emissions on ice formation processes in clouds results in large uncertainties in efforts to constrain the magnitude of current and projected climate impacts. This project will define the emissions of ice nucleating particles from soil and plant surfaces to the atmosphere, particularly to quantify the contributions and nature of organic particles, and within this group, biological particles, in comparison to known inorganic global ice nucleating particle sources, notably desert mineral dust particles. Results will be applicable toward improved quantification of ice nucleation processes in numerical modeling studies at cloud, regional, weather forecast, and climate scales.The project combines atmospheric and biological measurement tools toward defining the surface emissions of specific ice nucleating particle types from collected soil and plant samples, and toward recognition of their influence during direct atmospheric sampling. Laboratory studies will be performed of ice nucleation by collected soil particles and plant organisms subject to lofting by winds from regionally important ecosystems. Studies will have specific focus on soils, plants, and ecotypes of the intermountain West and Central U.S. Plains regions where aerosol cloud interactions may impact both water resources and severe storm characteristics, but methods and results will inform future land-based and airborne studies in other regions. Multiple methods will be used to measure the numbers of particles that freeze when they enter liquid drops at different temperatures, as they do in natural clouds, and these results will be related to total aerosol mass and surface area. Specialized tools will be applied to characterize the compositions of particles freezing, including electron microprobe analysis, single particle mass spectrometry, thermal and chemical treatments for selective removal of biological and organic particles, genetic amplification and sequencing of all biological particles, specific quantification of genes of known bacterial and fungal ice nucleating particles, and online measurements of fluorescent biological particles. These same tools will be applied toward detecting the presence and abundance of different ice nucleating particle types per volume of air in the atmosphere over plant and soil surfaces in collection areas before, during and after perturbations by wind, rain, and harvesting. Detailed and generalized descriptions of ice nucleation will be developed from these results for application in atmospheric models.The broader impacts of this work involve promoting postdoctoral education and training, development and testing of new instrumentation and methods, application of results toward climate change issues through collaborative numerical modeling studies, and fostering cross-disciplinary research between the atmospheric and biological sciences. Results are of critical importance to unresolved impact of aerosols on ice clouds and regional and global climate. Dissemination of results will occur via a project web site, publications, participation in conferences and scientific working groups and open communication with science news agencies.