Airport buildings affect the emitted point source plumes by essentially serving as obstacles to those sources, and therefore have a significant impact on concentrations resulting from stationary source emissions. Buildings have no effect on the concentrations estimated from volume and area sources such as aircraft, APU, GSE, roadways, and parking facilities. Secondly, given the nature of the airport environment, buildings tend to be short and thus the downwash effect tends to be subdued. AERMOD includes the PRIME plume rise and building downwash model which considers the position of the stack relative to the buildings, streamline deflection near the building, and vertical wind speed shear and velocity deficit effects on plume rise. EDMS/AEDT allows users to include building locations and dimensions and applies the effects of building downwash on AERMOD “point” sources only. Airport projects with significant stationary sources and large/tall buildings should consider conducting a building downwash analysis in consultation with regulatory agencies. 

## D.2.9 Receptor Locations 

The locations at which concentrations are estimated are known as “receptors”. EPA’s Guideline on Air Quality Models 88 provides guidance on the selection of receptor sites and recommends that receptor sites be placed to estimate the highest potential concentrations. 

Receptors are defined as those areas in which pollutant concentrations are to be calculated. If an overall view of pollutant concentration on and off the site is desired, then a grid of receptors should be defined. For many applications, however, only those locations defined as “sensitive” (i.e., where the public is likely to come into contact with emissions) may be modeled in order to reduce the model computational requirements 89 . For a complex emissions scenario such as an airport, reducing the number of receptors may be necessary for this reason. 

Nevertheless, pollutant concentrations should be predicted at a sufficient number of receptor locations to identify the maximum concentrations. Because EDMS/AEDT and AERMOD is designed to handle only a moderate number of receptors, a strategy must be developed to h elp limit the run time of the model while optimizing the results. Overall, the dispersion analysis should include about 50 receptors, selected as follows: 

• Boundary receptors – Boundary receptors should be located in areas along the airport boundary at a spacing of approximately 10 degrees (a total of 36 receptors). 

• Sensitive receptors – Sensitive receptors include schools, parks, residential areas, health/day-care centers located in the vicinity of the airport based on land use maps. 

• Worst-case receptors – Worst-case receptors should be selected in close proximity to air emissions sources such as near runway ends, terminal area access/egress roads, and off - 

