For suspension of particles due to vehicular traffic on unpaved contaminated surfaces, the emission rate is computed from
where
Eroad is the emission rate from road surfaces (g vehicle-1 km-1)
Lroad is the distance of travel over contaminated surface (km)
nv is the average number of vehicles traveling over the contaminated surface per day (vehicle d-1).
The factor of 365 in Equation 5.46 converts g d-1 into g yr-1.
The emission rate from road surfaces is simply the combination of suspension
from unpaved road surfaces and paved surfaces.
where
Eunpav is the emission rate for traffic on unpaved roads (g vehicle-1 km-1)
Epav is the emission rate for traffic on paved roads (g vehicle-1 km-1).
Formulations used to compute pollutant emissions per unit area resulting
from the mechanical disturbances by vehicle traffic are also based on Cowherd
et al. (1985). The pollutant emission caused by traffic moving over
unpaved surfaces is computed using
where
Psilt is the percent silt plus very fine sand (unitless)
vveh is the mean vehicle speed (km hr-1)
Mveh is the mean vehicle weight (Mg)
nw is the mean number of wheels on a vehicle (unitless)
np is the number of days with at least 0.254 mm (0.01 in.) of precipitation per year (unitless).
Site-specific information from local sources is normally obtained for each
of the parameters. When site-specific data are not available, the
default values given by Cowherd et al. (1985), which are listed in Table
5.9, may be used.
Values for np are obtained from a local source of meteorological
data. For a paved road, Epav is calculated using Equation
5.48. An additional assumption is made for paved roads; only 1% of
the road surface is covered with respirable material.
Table 5.9. Default Values for Independent Variables
of Equation 5.48(a,b)
Site
Psilt (%)
vveh (km hr-1)
Mveh (Mg)
nw (#)
Rural/Residential
15 (5-68)
48 (40-64)
2
4
Industrial
8 (2-29)
24 (8-32)
3
15
26
4
6
10
(a)
Based on Cowherd et al. (1985).
(b) Numbers in parentheses are ranges
of measured values.
