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NOAA and EPA Study Finds Highway Barriers May Reduce Pollutants as Well as Block Sound and Sight of Traffic

Barrier and instruments scientists used in the highway study. Click to enlarge.

Highway barriers erected along roadways to block the sound and sight of traffic for the adjoining neighborhoods may also be reducing the amount of pollutants, such as soot from diesel exhaust, reaching area residents, according to a study by NOAA and the US Environmental Protection Agency (EPA).

In the study, researchers released harmless “tracers”—gases that act as a stand-in for vehicle-related toxic pollutants such as carbon monoxide and heavy metals, and volatile organic compounds such as benzene—so scientists can “trace” their movement through the air.

The study, the first to systematically and comprehensively investigate the role of atmospheric stability in real world conditions on the movement of pollutants near highway barriers, is now online and will appear in a January 2010 print edition of the journal 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.

—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 human health effects such as respiratory disease, cardiovascular illness, and cancer in individuals living or working near heavily trafficked roadways. It is difficult to measure accurately and isolate the effect of highway barriers on the transport and dispersion of the pollutants that cause these health effects in real-world environments with a wide range of atmospheric conditions.

Researchers were able to conduct tracer studies in unstable, neutral and stable atmospheric conditions in tightly controlled circumstances, to quantify the effects of roadside barriers on pollutant dispersion. Atmospheric stability is a measure of top-to-bottom mixing in the atmosphere. The atmosphere is stable when the coldest air is at ground level. When there is no significant difference between temperatures in the top and bottom layers, conditions are neutral. Like a pan of boiling water, an unstable atmosphere roils as warm air rises from ground level.

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. The amount of pollutants was much higher on roadway areas flanked by barriers than in areas without them.

—Dennis Finn


  • Dennis Finn, Kirk L. Clawson, Roger G. Carter, Jason D. Rich, Richard M. Eckman, Steven G. Perry, Vlad Isakov and David K. Heist (2009) Tracer studies to characterize the effects of roadside noise barriers on near-road pollutant dispersion under varying atmospheric stability conditions. Atmospheric Environment in press doi: 10.1016/j.atmosenv.2009.10.012



Barriers don't reduce pollution, they concentrate it in a smaller area. Which sounds good, unless of course you have to use that road to get to work or school or the grocery store.

Dave R

Well, it seems fairly obvious - expose people living near major thoroughfairs to permanantly high pollution levels, or expose people creating the pollution to higher pollution levels.

I know what action I'd rather choose.

It'd be interesting to see if any natural barriers (such as dense trees or shrubs) also help reduce pollutant levels since many are known to reduce indoor pollutant levels.


It seems appropriate that pollutants should bounce back to the polluters, not the innocent neighbours.

With more pollutants concentrated directly over highways, drivers of gas guzzlers may take notice or ........ and/or suffer the consequences.


How about not zoning residences along known polluting byways and industrial areas??


Developers like to build close to highways to convince buyers that commuting is quick and easy. They never tell potential buyers that it is going to be a living hell.


Some Europeans put solar panels on the barriers, use some of that energy to filter the air. It would save lives and reduce illness.

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