Air pollutant transport and dispersion during a cold pool episode in the Mid Columbia Basin

Persistent wintertime cold pools are a prominent feature of the meteorology of many basin areas, leading to high static stability conditions that can trap air for many days and allow pollutants to build up to high levels. Forecasting the buildup and removal of these cold pools and the transport and diffusion of pollutants during cold pool evolution is difficult because the mechanisms leading to wintertime cold pool development, maintenance and removal are not yet clear. A three-dimensional high resolution mesoscale numerical model is used to simulate a cold pool episode observed in the winter of 1999 in Columbia Basin of eastern Washington. The modeled evolution of temperature and stability in the cold pool agree well with observations. Sensitivity tests are used to identify the mechanisms responsible for cold pool buildup and breakup. The implications for air pollution are illustrated using a Lagrangian particle dispersion model that is coupled to the mesoscale meteorological model. Particles are released to the pool and are tracked in space and time, illustrating how the cold pool evolution processes affect transport and dispersion of pollutants within the basin, and how pollutants are released from the basin as the cold pool is destroyed.