treasure valley road dust study: final report - ResearchGate

PM 10 and PM 2.5 by DustTrak and particle counts per size bin were averaged for the left and right
inlets.
In the Treasure Valley, a 440 m section of road was selected for testing. Passes were run
over the same range of speeds as in Fort Bliss tests. The same lane of travel was surveyed with
the vehicle traveling in both northbound and southbound directions. Using this approach, both
the left and right inlets sampled the same tracks on the road. Values were averaged over each
pass.
The resulting values from both sets of tests were regressed against the vehicle speed
using a power function:
T
* b
T
? TB
? T s
( 2 )
where T T is the aerosol concentration at the vehicle tire, T B is the background aerosol
concentration at the bumper inlet, and s is the speed of the vehicle. The parameters T * and b
were iteratively calculated by minimizing the least squares error between the observed and
predicted values.
Figure 3-15 shows the example of the regression for DustTrak PM 10 measurements from
the Treasure Valley speed tests. In this example, speed explains 97% of the variability of the
average measurement from each vehicle pass. The remaining measured parameters (i.e. PM 2.5 ,
and particle counts for each size bin) were also regressed against vehicle speed. The exponents
of these regressions and the percentage of variance explained by the speed term are shown in
Table 3-2. Note that T * in Eq. (2) is a measure of the inherent “dirtiness” of the road.
Figure 3-15. Relationship between differential Dustraks measurements and vehicle speed for tests conducted
on a common road section in the Treasure Valley, Idaho. R 2 = 0.97.
3-15