| Title | Issues Affecting Dispersion Near Highways: Light Winds, Intra-Urban Dispersion, Vehicle Wakes, and the Roadway-2 Dispersion Model |
|---|---|
| Record ID | 75204 |
| Personal Name Creator |
Rao, K. S.; Hosker Jr., R.P.; Gunter, R.L.; Nappo, C.J.; Meyers, T.P.; Birdwell, K.R.; White, J.R. |
| Corporate Creator | United States. Federal Highway Administration |
| Corporate Contributor |
United States. National Oceanic and Atmospheric Administration |
| Publisher | United States. Federal Highway Administration |
| Publication Date | 20030201 |
| Language | English |
| Abstract | The research described in this report is a collaboration between the National Oceanic and Atmospheric Administration's (NOAA) Atmospheric Turbulence and Diffusion Division (ATDD) and the Federal Highway Administration (FHWA). The FHWA must perform assessments of the likely impacts of traffic-related air pollutants near highways. Urban highways are a particular concern, and introduce a range of complications, particularly uncertainties about the wind and turbulence information needed to drive the air quality models. This research covered several tasks. The first was a thorough study of light wind data, stratified by wind speed category and time of day, using observations from a number of research-grade meteorological networks in different locations around the U.S. The instruments in these networks could resolve winds down to about 0.5 mls. Data from the humid and vegetation-covered southeastern U.S., the arid northwest, and a coastal environment were those considered in the most detail. The results are covered in considerable detail. Winds and turbulence within urban regions are of considerable interest, but relatively few measurements are available. Data were therefore collected using 3-D sonic anemometers in Knoxville and Nashville, TN, as well as at nearby rural sites. The mean and turbulence quantities and spectra were compared, to examine the ability to use data from airports or other rural observing locations in lieu of intra-urban data. There are few data available on the wakes of vehicles, which are known to affect the initial dispersion of vehicular effluents, especially under light wind conditions. Most available data are from wind tunnels. To provide real-world data, a special towable apparatus was constructed, which supported six 3-D sonic anemometers for simultaneous measurements at different locations within the wake of the tow vehicle. Turbulent kinetic energy (TKE) was calculated at a number of locations in the near wake, and contours of TKE were plotted. Flow vectors for various cross-sections of the wake were determined. A new near-highway dispersion model was developed, called ROADWAY -2. The model is based on the U.S. Environmental Protection Agency's (EPA) ROADWAY model, but it uses a TKE closure formulation for a time-varying atmospheric boundary layer to provide the mean wind and temperature profiles from input meteorological data. It allows the use of on-site turbulence data, which is increasingly feasible given recent instrumentation advances and lower costs. The parameterization of vehicle wake effects is also new, based on canopy flow theory and wind tunnel measurements. Comparisons of predicted and observed concentrations from the General Motors field study are generally good. More than 80% of the model predictions were within a factor of two, and 95% were within a factor of five. Suggestions for future research are provided. |
| Rosap ID | dot:49982 |
| Rosap URL | https://rosap.ntl.bts.gov/view/dot/49982 |
| TRT Terms | Air pollution; Mobile sources; Wakes; Wind; Mathematical models |
| General Subjects | Dispersion; Weather; Vehicle wakes; Wind; Urban turbulence; Pollutant dispersion |
| Geographical Coverage |
United States |
| Report Number | FHWA-RD-01-030 |
| Resource type | Tech Report |
| URL | https://ntlrepository.blob.core.windows.net/lib/75000/75200/75204/FHWA-RD-01-030.pdf |
| Format | |
| Database | NTL Digital Repository |