## E.2.5 Select Receptor Site Locations 

The locations at which concentrations are estimated are known as “receptors”. EPA’s Guideline on Air Quality Models 105 provides guidance on the selection of receptor sites and recommends that receptor sites be placed to estimate the highest potential concentrations. 

When completing a CO hot-spot analysis, receptors should be placed at each approach on both sides of the roadway where traffic queues develop (i.e., at least three meters from each of the traveled roadways which make-up the intersection). Other examples of reasonable receptor sites include the following: 

• Sidewalks to which the general public has access on a continuous basis; 

• A vacant lot near an intersection, where the general public would have continuous access; 

• Portions of a nearby parking lot to which pedestrians have continuous access; 

• In the vicinity of parking lot entrances and exits, provided a nearby area contains a public sidewalk, residences, or structures to which the general public is likely continuous access; and 

• Property lines of residences, hospitals, rest homes, schools, playgrounds, and entrances and ground-level air intakes to all other buildings. 

For further guidance on the selection of receptor locations for CO hot -spot analyses, refer to EPA’s Guideline for Modeling Carbon Monoxide from Roadway Intersection 106 . 

Additionally, the selection of receptor sites for PM hot-spot analyses should be determined on a case-by-case basis taking into account project -specific factors that may influence areas expected high concentrations, such as prevailing wind directions, monitor locations, topography, and other factors. Typically, receptors should be sited as near as five meters from a source (e.g., the edge of a traffic lane or a source in a terminal. For further guidance on the selection receptor locations for PM hot-spot analyses refer to EPA’s Transportation Conformity Guidance for Quantitative Hot-spot Analyses in PM$_{2.5 }$and PM$_{10 }$ Nonattainment and Maintenance Areas mentioned above. 

EPA recommends that receptors s hould be positioned to represent concentrations near -ground level, generally at a height of 1.8 meters (approximately 6 feet) above grade. Receptors should also be placed at higher elevations (if needed) to represent concentrations at different heights along multi-story buildings, such as apartment or office buildings. 

Finally, when completing air quality modeling for Build and No-B uild scenarios, receptors should be placed in the same locations in both scenarios so that direct comparisons can be made between the concentrations calculated at each receptor. 

