treasure valley road dust study: final report - ResearchGate

important to note that the experiments at Ft. Bliss were conducted during daylight hours on a flat,
sparsely vegetated landscape and that dust fallout was only measured for distances up to 50
meters from the road. Clearly, dense vegetation and stable nighttime winds may have an effect
on dust removal rates. Longer range transport on the order of 1 to 5 km from the point of
emission may also result in significant removal of dust particles. Model results from the TVRDS
indicated that the removal of particles by impaction is an extremely important pathway for the
diminishment of horizontal fluxes of road dust PM 10 . The model suggested that the fluxes of
dust across a horizontal plane continue to decrease appreciably with downwind distances on the
order of a kilometer. From the standpoint of emissions and regional scale air quality models, this
means that using the emissions factors measured at the side of a road (such as is done in AP-42
as well as the current study) for input in urban or regionalscale air quality models can result in a
substantial over-prediction of the contribution of road dust to ambient PM 10 .
8.6 Areas for Future Research
Future research should focus on the processes that affect dust removal during transport
from roads to ambient air quality monitors and the factors that affect the potential of a road to
emit dust. A disconnect still exists between the estimates of dust emissions from roads and the
amount of dust that is found on filters from ambient PM 10 samplers. In particular, the effects of
vegetation and atmospheric stability conditions on the removal of dust should be investigated.
Future tower studies should also examine the horizontal fluxes of dust far from the emissions
source (1 – 5 km).
The results of this study showed that the potential of a road to emit dust is related to
several factors such as speed, season, and setting. While it is important to know these
parameters, it is equally important to understand the mechanisms of where road dust originates
from and how it is removed. The TRAKER has been a useful tool in allowing for assessment of
some of the factors that contribute to dust emissions. In future studies, data points should be
documented and flagged in real-time so that individual measurements are associated with a
specific set of road conditions including whether or not the shoulders are paved, the lane of
travel of the TRAKER, and the coincidence of a dust-source ingress/egress such as an unpaved
road or a construction site.
Re-assessment of the TRAKER signal horizontal flux calibration under paved road
conditions is needed. The work performed at Ft. Bliss has demonstrated the utility of using real -
time particle sensors for measuring emissions. These measurements should be repeated to obtain
more accurate emissions factors for paved roads. Similarly, the relationship between emissions
and vehicle weight should be revisited to determine more accurate factors for a variety of vehicle
types.
Road dust is a significant source of PM 10 in the Western United States. However, there is
little hard evidence to support the effectiveness of mitigation measures. Therefore, states or
counties that are having difficulty meeting the National Ambient Air Quality Standards are
forced to implement measures that have uncertain benefits. The most important of these
measures is street sweeping. Most metropolitan areas use street sweepers to keep gutters and
curbs free of debris. The EPA allows some emissions credits for the use of street sweepers as
mitigation of road dust emissions. The effectiveness of street sweepers in reducing PM 10
emissions remains questionable. It is important to comprehensively evaluate the ability of street
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