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Modeling Dispersion of Emissions from Depressed Roadways
Seyedmorteza Amini1, Faraz Enayati Ahangar1, David K Heist2
1Department of Mechanical Engineering, University of California, Riverside, CA 92521, USA.
Atmospheric Environment (Oxford, England : 1994)
|September 20, 2019
Summary
This study analyzed wind tunnel data for depressed roadways, finding that modified flat terrain models can accurately predict downwind emission concentrations. These adjustments improve dispersion modeling for complex highway geometries.
Area of Science:
- Environmental Engineering
- Atmospheric Science
- Fluid Dynamics
Background:
- Depressed roadways create complex airflow and turbulence.
- Standard dispersion models often fail to accurately predict pollutant concentrations near these structures.
- Understanding emission dispersion is crucial for air quality assessments.
Purpose of the Study:
- To analyze pollutant dispersion from various depressed roadway configurations using wind tunnel data.
- To adapt existing flat terrain dispersion models for use with depressed highways.
- To propose modifications for line-source dispersion models to better represent depressed roadway emissions.
Main Methods:
- Wind tunnel experiments were conducted on three depressed roadway designs.
- A flat terrain dispersion model (van Ulden, 1978) was adapted.
- Modifications were incorporated into the RLINE line-source dispersion model (Snyder et al., 2013).
Main Results:
- Depressed roadways decrease surface concentrations compared to at-grade configurations.
- An adapted flat terrain model with increased vertical dispersion and friction velocity explained observed concentrations.
- A vertical distribution function with an exponent of 1.3 best described concentration profiles under neutral conditions.
- The RLINE model, with modifications, provided acceptable near-surface concentration estimates, but its Gaussian distribution (exponent 2) was inadequate for higher elevations.
Conclusions:
- Modified dispersion models can accurately estimate pollutant concentrations from depressed highways.
- A simple method involving two parameters modifying vertical plume spread is proposed for models like RLINE and AERMOD.
- These findings enhance the accuracy of air quality modeling for complex highway environments.
