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Implications of Aerosol Physicochemical Properties Including Ice Nucleation at ARM Mega Sites for Improved Understanding of Microphysical Atmospheric Cloud Processes

Active Dates 9/1/2018-8/31/2024
Program Area Atmospheric System Research
Project Description
A specific subset of atmospheric particles can act as ice-nucleating particles (INPs) in mixed-phase clouds and, ultimately, influence precipitation and the Earth’s radiative energy balance. Despite the importance of INPs, current ambient INP data derived from field measurements are not well interpreted with detailed aerosol and cloud properties, except for a few short-term field studies. This project will fill this gap by using long-term measurements from DOE’s Atmospheric Radiation Measurement (ARM) sites, complemented with robust and well-characterized INP measurements that will be archived in the ARM database. Detailed ARM observational data of aerosol chemical composition speciation, abundance, cloud condensation nuclei activity, and hygroscopicity are of the utmost importance for better understanding of INP mixing states, as well as their implication in cloud, precipitation, and regional weather patterns. The proposed new INP measurements will experimentally characterize abundance and physicochemical properties of ambient INPs at the ARM Southern Great Plains (SGP), Eastern North Atlantic (ENA), and North Slope of Alaska (NSA) atmospheric observatories. A combination of a new in situ expansion chamber and the offline droplet freezing assay technique for INP measurement, as well as microspectroscopic characterization techniques, will be used to elucidate abundance and physicochemical properties of ambient INPs at the above-mentioned ARM observational sites. Different INP episodes (agricultural, marine biogenic, and Arctic at SGP, ENA, and NSA, respectively) will be assessed and evaluated to help understand convective and mixed-phase cloud systems typically observed in these regions. The proposed research will generate data to understand how particle chemical composition and mixing state influence ambient ice nucleation propensity at the ARM sites. Such datasets have long been a missing piece in the study of cloud microphysics and atmospheric chemistry, and are of importance to improve atmospheric models of cloud feedback and to determine their impact on the global radiative energy budget. Currently, ice formation processes are very poorly represented in weather and earth system models, including DOE’s Energy Exascale Earth System Model (E3SM), and this study will support the DOE mission by providing INP parameterizations representative of the ARM sites. To constrain E3SM, this project will produce a variety of INP parameterizations, such as ice nucleation active surface site density, cumulative number concentration of INPs per volume of air, and water activity-based freezing descriptions.

Award Recipient(s)
  • West Texas A&M University (PI: Hiranuma, Naruki)