Meteorological conditions and orographic features cause elevated pollutant concentrations in multiple cities in the western U.S. (e.g., 24-hr particulate matter concentrations ~90 μg m-3). The complex mountainous terrain in these regions along with favorable meteorology leads to the formation of cold air pools (CAP), where cold dense air settles on the valley floor. During wintertime, persistent multi-day CAPs can form when background winds are weak, or stagnant, due to slow moving high-pressure systems. The atmospheric boundary layer is strongly stable during CAP events, leading to a decrease in planetary boundary layer height and inhibited turbulent mixing, both of which contribute to elevated air pollution concentrations. Recent research has shown that numerical weather prediction models can capture the synoptic weather patterns associated with CAP formation and destruction. However, the models do not capture the small scale turbulent mixing or heat fluxes near the earth’s surface, therefore impacting simulation results related to the land-atmosphere exchange of heat, moisture, and momentum. Additionally, this small scale mixing process is responsible for the turbulent mixing of pollutants in the atmospheric boundary layer. The surface-atmosphere exchange is over-estimated during CAP events, which leads to under-estimated pollutant concentrations. This talk will present recent observations of turbulent fluxes and surface energy balance closure, quantified for seven land use types in the Salt Lake Valley, Utah. The turbulence observations and surface energy balance closure are used to investigate the relationship between decreased turbulent mixing and pollutant accumulation during wintertime persistent CAPs. Results from the Weather Research and Forecasting model will also be presented to compare simulated surface fluxes with observations.
Speaker Bio: Heather Holmes is an Assistant Professor in the Department of Physics and Atmospheric Sciences Program at University of Nevada, Reno. Her PhD research focus was experimental investigations to study air pollution, turbulence, meteorology, and chemistry in the atmospheric boundary layer. She has three years of postdoctoral training, including two years at Georgia Tech where her focus was to analyze air pollution and air quality modeling data to better understand how emission sources combine to impact air quality and to develop exposure metrics for spatial health studies and time-series epidemiologic analyses. Her current research group, the Atmospheric Turbulence and Air Quality Laboratory (www.unr.edu/~hholmes), uses numerical weather prediction, chemical transport modeling, and satellite remote sensing combined with ground-based monitors to investigate air pollution transport and provide data for human health and public policy assessments.
Heather Holmes, Assistant Professor
Atmospheric Sciences Program
Department of Physics, LP 205
University of Nevada, Reno