treasure valley road dust study: final report - ResearchGate

W = Mean vehicle weight (tons).
M = Surface material moisture content. (%)
This latter formulation of the emissions factor is not used in current inventories and is a subject
of controversy because there is clearly a relationship between vehicle speed and emissions in
most reported tests.
A control effectiveness modifier due to precipitation is often appended to the unpaved
road emission factor equation to estimate annual averages:
P annual,county = PrecipDays/365
where PrecipDays is the number of days per year with greater than 0.01 inches of precipitation.
This modifier assumes 100% emissions reduction effectiveness for each day with more than 0.01
inches of precipitation.
For paved roads, the U.S. EPA (1999) emission factor is:
Eq. 2-3 EF 10 = k?(sL) 0.65 ?(W) 1.5
where:
k = paved road dust emissions factor multiplier for PM 10 : 0.56 g/VKT or 0.9 g/VMT.
sL = silt loading of the surface material (g/m 2 ).
W = mean vehicle weight (tons)
Note that the size fraction is incorporated into the emission factor and that the silt loading
rather than the fraction of silt is used. There is no dependence of the paved road dust emission
factor on vehicle speed or number of wheels as there is in Eq. 2-1 for unpaved road emissions.
2.1 Methods
2.1.1 Site Selection
Sites for silt sampling were selected to encompass each of four road types, arterial,
collector, local, and unpaved, in both Ada and Canyon Counties. Table 2-1 and Table 2-2 list the
sample locations and the amount of road dirt that was obtained at each site in winter 2001 and
summer 2001, respectively. Figure 2-1 shows where the silt samples were obtained in the
Treasure Valley. Detailed maps for each of the sites are provided in Appendix A. Silt samples
from paved and unpaved roads were obtained and analyzed according to the instructions in
Appendices C1 and C2 of AP-42 (USEPA, 1999).
2.1.2 Sample procurement
Sampling on paved roads required the closure of one or more lanes of traffic. Lane
closure permits were obtained from the appropriate municipalities prior to road sampling. At
each of the nine paved road sites, three sections of a travel lane were measured, marked off with
tape, and documented with the aid of a GPS receiver. Wherever possible, the centers of the road
sections were distanced a minimum of 15 m apart to allow for a more representative sample.
Sections ranged from 2.6 m to 4.6 m in width (cross-lane direction) and from 0.3 m to 9 m in
length (along-lane direction). The width of the sections was determined by including the portion
of the lane where vehicle tires travel under normal driving conditions and excluding road
shoulders, centerline dividers, and other portions of the road that are not normally traversed by
2-2