Taxipaths (i.e., the arrival path from the end of the landing roll to the terminal and the departure path from the terminal to the runway end) are also designated based on field observations, airport procedures, and/or airfield simulation modeling and included in the dispersion modeling analysis. In this manner, a taxipath is a series of taxiways from runway end to aircraft servicing location. Within these taxipaths, aircraft speeds can be designated as 5 knots within the terminal areas, 10 knots within taxiways with tight turns, 15 knots for most remaining taxiways, and 35 knots for high speeds runway exits. The EDMS/AEDT default value is 15 knots. 

Apron/gate areas define the locations of aircraft operations such as unloading and loading of cargo and passengers. Thus, these locations also represent activities associated with APU, GSE and other supporting operations. 

## D.2.6 Temporal Profiles 

Temporal (or operational) profiles are used to describe the relationship of one time period another (i.e., the relationship of the activity during 1-hour to the activity during a twenty-four hour period). In EDMS/AEDT, these temporal profiles are used to represent varying levels of activity as a fraction of a peak period (a scale of zero to one: unless values denoted as fraction of peak values). 

Notably, distinct temporal profiles can be developed for air carrier, cargo, commuter, general aviation, and military aircraft operations during arrival and departure conditions for each quarter hour of the day, day of the week, and month based on ASPM data. 

## D.2.7 Topographical Data 

The terrain in the vicinity of airports is usually flat because of the requirement for a runway, approach and climbout area. Some sources, such as training fires, stacks, and painting operations, produce emission in the form of a buoyant plume. In such cases, topography may play a role in altering the downwind dispersion of the plume and should be included in dispersion analysis. 

AERMOD includes a terrain preprocessor, AERMAP 87 , which provides a physical relationship between terrain features and the behavior of air pollution plumes. AERMAP processes USGS Digital Elevation Model (DEM) data and creates a file of elevation and hill- height scaling factors. AERMAP generates location and height data for each receptor and source location. also provides information that allows the dispersion model to simulate the effects of air flowing over hills or splitting flow around hills. 

## D.2.8 Building Downwash 

Building downwash describes the effect that wind flowing over or around a structure(s) has on plumes released from nearby sources (such as stacks). Essentially, structure(s) create a cavity of recirculating winds in the area near the structure(s), and these cavities cause increased vertical dispersion of plumes emitted from sources on or near the structure(s). Building downwash often leads to elevated concentrations downwind of affected sources. 

