The Introduction of a new aerosol emissions parameterization scheme into RAMS

A new aerosol source parameterization scheme was implemented into the Colorado State University Regional Atmospheric Modeling System (RAMS). This parameterization was developed to replace the need for WRF Chemistry output in predicting atmospheric CCN concentrations. In this parameterization, aerosol is sourced at a fixed rate into the model at two vertical levels surrounding a prescribed height. The geographical mapping of aerosol is derived from the surface aerosol output after a one-hour WRF Chemistry simulation. The model represents aerosol chemistry by using estimates of the hygroscopicty parameter κ derived from WRF Chemistry. A comparison of this parameterization to CCN data collected at Mesa Verde National Park (MVNP), during the Inhibition of Snowfall by Aerosol Pollution (ISPA) III field campaign has shown reasonable accuracy in predicting near surface CCN concentrations. While this parameterization has proven only marginally more accurate than the previous method using WRF Chemistry output, it is much more computationally efficient. For identical simulations, a reduction in computer time of ~85% is typically observed when using RAMS vs. WRF Chemistry. Furthermore, containing the emission and transport of aerosol entirely within RAMS removes inaccuracies that arise from discrepancies in model physics between WRF and RAMS. This scheme will be used, primarily, for simulations of orographic snowfall events in western Colorado in order to gain a better understanding of the impact pollution aerosol has on the water resources within this region.