Environmental Engineering Reference
In-Depth Information
existing models and data bases related to near road dispersion; (2) Developing
measurement methods - developing methods for measuring near-road con-
centration distributions in both the laboratory and in actual urban situations;
(3) Performing new studies - collecting and analyzing field, tracer, and wind
tunnel measurements, as well as CFD results to understand the basic structure of
flow and dispersion; and (4) Improving algorithms and modeling methodologies -
developing and evaluating improved algorithms and incorporating them into a
selected near-field modeling platform (e.g. AERMOD) and as a sub-grid algorithm
within CMAQ.
Examining existing tools: An exhaustive review of 21 available dispersion
models that simulate line-type sources was completed (Pierce et al., 2008). Based
on the findings and recommendations of this report, AERMOD (Cimorelli et al.,
2005; Perry et al., 2005) was chosen as the best platform for further development
for roadway scenarios. AERMOD is the current near-field and urban scale model
recommended by the EPA for regulatory assessments.
Developing measurement methods: Isakov et al. (2007) describe and demon-
strate a methodology using mobile platform measurements in Wilmington, Delaware
to characterize fine particulate and formaldehyde concentrations. This methodology
has been adopted by EPA and is being used with an electric mobile sampling
vehicle in a series of intensive field studies in Las Vegas, Detroit, and Durham
(NC) for examining the impact of roadside barriers on local air quality and their
potential use for pollution mitigation.
Performing new studies: Experiments in EPA's meteorological wind tunnel have
examined the flow and dispersion around a variety of roadway features (e.g.
barriers, road cuts). Clawson et al. in this issue report on a tracer study of line-
source emissions upwind of a single 6-m high wall typical for a road noise barrier.
Also, field measurements have been made along an eight-lane expressway in
Raleigh, NC, examining the concentration gradient in a clearing and behind a
noise barrier that showed the substantial influence of the barrier on concentration
distributions.
Improving algorithms and modeling methodologies: Cook et al. (2008) des-
cribe an approach for developing detailed highway emission inventories based on
emission factors and traffic inventories for individual road links. Applying a line-
source model of Venkatram et al. (2007, 2009), the eight-lane expressway in the
Raleigh 2006 field study was simulated for an area with no terrain changes or
obstructions to the flow. The concentration gradient for benzene was matched well.
Results of EPA wind tunnel studies provide initial indications that for distances
beyond the cavity zone of the barrier, the effects of noise barriers can be simulated
with a no- barrier model by adjusting the effective source location upwind by a
distance of 5-10 barrier heights (Heist et al., 2008). Based on previous wind
tunnel studies, an algorithm is being developed for inclusion into AERMOD for
Search WWH ::




Custom Search