Dr. Cari S. Dutcher was awarded an Atmospheric and Geospace Sciences Postdoctoral Research Fellowship to conduct a research project with Anthony Wexler at the University of California at Davis (UCD). Dutcher will employ a statistical thermodynamic approach to the uptake of atmospherically important species onto particles that are important in the air, such as black carbon, organics and water-containing aerosols. The thermodynamic treatment of aerosol properties will be extended to conditions found in the upper troposphere, with low temperatures (relevant to higher altitudes and latitudes) and at low relative humidity (relevant to arid climates and some higher altitude situations). Results will enhance thermodynamic predictions of the Extended Aerosol Inorganics Model (E-AIM) and will improve understanding of (1) the interactions of gases, particles, aerosols and water in the earth's atmosphere, (2) the modification of thermodynamic properties in the cold, dry arid conditions found in the upper troposphere and (3) the impact, both direct and indirect, sorption processes have on the role of particles in climate.
Dutcher will also develop a web-based model calculator to enable those who are not experts in atmospheric thermodynamics to make effective use of models for practical calculations. Dutcher will integrate research and education through mentorship of undergraduate researchers and by engaging in interactive environmental and conservational demonstrations at local schools. The project will also support the outreach programs currently underway at the Air Quality Research Center at UCD, hosting activities from high-school group tours to international conferences in air quality and climate change. Several activities would be aimed at young girls.
Accurate predictions of water and solute activities in atmospheric aerosols to very low equilibrium relative humidities (RH) are central to predications of aerosol size, optical properties, cloud formation and climate change. However, atmospheric aerosol particles exhibit highly complex behavior and heretofore lacked a comprehensive thermodynamic model, especially at low RH. Previous activity coefficient models commonly used in atmospheric science are highly parameterized, leading to two shortcomings: First, beyond the concentration range of the available data, these models behave un-physically since they have no fundamental thermodynamic underpinning for highly supersaturated situations that are common in the atmosphere. Second, these models require solute-solute interaction parameters, leading to an ever-increasing number of parameters that may not be identifiable for complex multi-component systems. This project addressed these shortcomings through integrating concepts from the fields of solution chemistry, electrostatics, and gas adsorption, resulting in a unified statistical thermodynamic treatment of atmospheric aerosols over the entire solute concentration range. Gibbs free energy, solvent and solute activity, solute concentration, as well as interfacial energies were derived. The model contains few adjustable parameters per solute, and zero ternary mixing parameters. The binary solute parameters can be estimated from the physical and electrostatic properties, if available, of the solution constituents or fit directly to osmotic and activity coefficient or surface tension data. When compared to existing activity models that have been extended to electrolyte containing solutions, the resultant thermodynamic model is found to yield unprecedented agreement of the solute concentration, osmotic coefficients and surface tension for solutions over the entire solute concentration range, with fewer parameters. The model has been applied to electrolyte and organic containing solutions and mixtures, to bulk and interfacial thermodynamic properties, and to single and, for bulk properties, multicomponent systems. For all of these systems, the model is valid over the entire range of relative humidities (i.e., 0 to 100%), potentially allowing for significantly more accurate atmospheric aerosol particle phase partitioning modeling efforts under atmospherically relevant conditions. This postdoctoral fellowship also supported many outreach and mentorship activities. I have had the opportunity to mentor undergraduate students, serve on outreach and career development panels, judge local scientific poster competitions, participate in cross-disciplinary student and postdoctoral seminar series, and speak at events serving underrepresented groups. As a postdoctoral scholar, I have also had the advantage to grow as a scientist and academic, primarily through being mentored by and forming new collaborations with colleagues both locally and abroad. I have also benefited through participation in the NSF postdoctoral fellows workshop, society-level short course training events, university-hosted grant writing workshops, as well as through sharing the research results at numerous conference presentations and on-campus interview visits. The achievements and training supported by this postdoctoral fellowship have equipped me with the confidence and skill needed to be successful in my new position as Assistant Professor of Mechanical Engineering at the University of Minnesota, Twin Cities.
