As stated in the Guideline on Air Quality Models, the AERSCREEN Model is a screening version of a preferred model, namely, the AERMOD model. AERSCREEN is designed to provide conservative (erring on the high side) estimates of air concentrations due to a single source. The Guideline goes on to say that AERSCREEN is the recommended model for most applications in all types of terrain and for considering building downwash. Applications of AERSCREEN in flat to rolling terrain are generally assessed with considering any elevated terrain in the vicinity of a source. The meteorological preprocessor associated with AERSCREEN called MAKEMET generates a matrix of hourly meteorological conditions with a range of temperatures, wind speeds, user-specified surface parameters, cloud cover, solar elevation angles, and mixing heights. Wind directions are always for every hour from the west. AERSCREEN handles a variable wind direction for source-building configurations by rotating the configuration every ten degrees. But the model looks in every 10 degree direction for terrain assuming the same MAKEMET meteorology applies in every direction. Because AERSCREEN interacts with the terrain preprocessor called AERMAP, the consideration of all elevated terrain is thus characterized. However, if specific directions where terrain is not as elevated in some sectors rather than others, a single AERSCREEN run will not suffice. This paper addresses and demonstrates how to apply AERSCREEN in a combined fashion to determine impacts in elevated nearby terrain as well as flatter to rolling terrain in the same vicinity but in different directions.
