Idealized modeling study of pollution transport over Alpine terrain

The Regional Atmospheric Modeling System (RAMS) is used to perform simulations of pollution transport within an idealized 2D valley in order to investigate the influence of various parameters on the slope winds and the resulting particle dispersion. The study is motivated by aerosol lidar measurements, conducted during the project INNAP in the Inn Valley, Austria, during winter 2007. Hence, the model topography is chosen in close resemblance to the Inn Valley, concerning its height, steepness, and orientation. An initially stagnant atmosphere ensures that particle dispersion is caused mainly by the local slope-wind system, which develops in the daytime due to solar irradiation. It is shown that this idealized setup is capable of producing qualitatively some of the flow structures, that lead to the observed particle distributions. Simulations with modified initial atmospheric stratifications illustrate in more detail the way how near-surface or elevated inversion layers affect the evolving slope winds, the entire wind field of the valley atmosphere, and therewith pollution transport. Further sensitivity tests investigate the influence of solar irradiation by means of varying valley orientation and surface conditions, including snow cover.