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 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.  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:  88 Appendix W to Part 51 – Guideline on Air Quality Models, http://www.ecfr.gov/cgi-bin/text- idx?SID=e6a5b817b94abf58460f48c032d9a39c&node=40:2.0.1.1.2.23.11.5.37&rgn=div9.  89  Some receptors are considered more sensitive to air pollutants than others, because of preexisting health  problems, proximity to the emissions source, or duration of exposure to air pollutants. Land uses such as  primary and secondary schools, hospitals, and convalescent homes are considered to be relatively sensitive to  poor air quality because the very young, the old, and the infirm are more susceptible to respiratory infections  and other air quality related health problems than the general public. Residential areas are also considered  sensitive to poor air quality because people in residential areas are often at home for extended periods.  Recreational land uses are moderately sensitive to air pollution, because vigorous exercise associated with  recreation places a high demand on respiratory system function.  83$_{ }$ • 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 - D.2.9  Receptor Locations  APPENDIX D$_{ }$