Highway barriers erected along roadways can be perceived as massive monuments to the future and were intended to block the sound and sight of traffic for the adjacent neighborhoods. They may do a bit more in terms of air borne pollution. In a study by NOAA and the US Environmental Protection Agency, researchers released harmless “tracers” to measure the potential movement of pollutants such as carbon monoxide and heavy metals, and volatile organic compounds such as benzene. The results showed a significant reduction for those neighborhoods in pollutants as a result of the barriers.
Highway barriers were originally designed to help block highway noise as well as to improve the view for nearby residents. At first the barriers were somewhat ugly but many now have vines and other vegetation softening the aesthetic effects.
The NOAA study is the first designed to scientifically study and evaluate the effects and role of the movement of air borne pollutants near highway barriers. The full report is to be on line in a January 2010 print edition of Atmospheric Environment.
“While the barriers block the noise and view of hundreds of vehicles whizzing by, we found that they also reduce high concentrations of pollutants from those vehicles by lifting and channeling them away from the adjoining areas, often a residential area,” said Dennis Finn, lead author and a research meteorologist at NOAA’s Air Resources Laboratory in Idaho Falls, Idaho.
A large body of research shows a variety of potential human health effects such as respiratory illness, cardiovascular effects, and cancer in individuals living or working near heavily traffic. Reduction in air borne pollution will have a positive effect on nearby residential neighborhoods.
Researchers were able to conduct studies in unstable, neutral and stable atmospheric conditions to quantify the effects of roadside barriers on pollutant dispersion. Atmospheric stability is a measure of how much atmospheric mixing is happening. Unstable (such as a windy day) cause maximum mixing and reduction in pollution levels while stable (a day with low or no wind) produces minimal mixing and pollution concentrations stay higher longer.
“We also found that the barriers tended to trap pollutants in the area of the roadway itself, especially at night in low wind speed conditions,” Finn said. “The amount of pollutants was much higher on roadway areas flanked by barriers than in areas without them.”
The study ultimately concluded that the barriers concentrate pollutants on the highway side especially when atmospheric conditions were stable.
Article by Andy Soos, appearing courtesy of ENN