Local and urban scale modeling - Air Pollution Modeling and Its Application - page 22

1.5 NOAA EPA Near-Roadway Sound Barrier
Atmospheric Tracer Study 2008

Kirk L. Clawson 1 , Dennis Finn 1 , Roger G. Carter 1 , Jason D. Rich 1 ,
Richard M. Eckman 1 , Steven G. Perry 2 , Vlad Isakov 2 , David K. Heist 2 ,
and Thomas Pierce 2

1

Air Resources Laboratory, Field Research Division, National Oceanic and Atmospheric
Administration, Idaho Falls, ID, USA
2

Atmospheric Modeling and Analysis Division, U.S. Environmental Protection Agency,
Research Triangle Park, NC, USA

Abstract A roadway toxics dispersion study was conducted at the Idaho National
Laboratory to document the effects on concentrations of roadway emissions behind
a roadside sound barrier in various conditions of atmospheric stability. The key
finding was that reduced concentrations were measured behind the barrier in all
stability conditions. It was also found that the magnitude of the concentration foot-
print behind the barrier was tied to atmospheric stability and that the roadway
tended to trap high concentrations during light wind speed conditions.

Keywords Wake zone, traffic emissions, pollutant dispersion near roadways,
concentration deficits, atmospheric tracer, atmospheric stability

1. Introduction

Numerous studies have found that living and working near roadways are associated
with a wide range of pathologies arising from the elevated levels of pollution
associated with vehicular emissions (e.g. Baldauf et al., 2008a). Given that noise
barriers and vegetation are now common roadside features it is pertinent to ask
what effect they might have on pollution levels adjacent to roadways. Many studies
have examined this issue. Some of these studies suggest that a barrier results in a
well-mixed zone with lower concentration extending downwind behind the barrier
(e.g. Baldauf et al., 2008b; Nokes and Benson, 1984; Bowker et al., 2007).
Some uncertainties persist, however, regarding the effects of roadside noise
barriers on pollutant concentrations in surrounding areas. Specifically, the role of
atmospheric stability has not been investigated in any systematic manner. Wind
tunnel studies are done in neutral stability conditions and most of the field experi-
mental work has been done during the daytime. Furthermore, much of the field
work has been done in “natural” settings featuring moving traffic and the associated