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u' =0.053 u a <br /> where: <br /> EF = emission factor(g/m2/yr) _ <br /> k = aerodynamic particle size multiplier(0.5)dimensionless <br /> P = erosion potential (g/m2) <br /> N = number of disturbances (366 disturbances per year) <br /> U. = friction velocity (m/s) <br /> U,* = threshold friction velocity (1.02 m/s) <br /> U10 = wind at reference height of 10 m(19 m(s) <br /> The basis of this methodology is that wind-blown dust from exposed areas will occur only when <br /> two conditions are met: the surface of the exposed area is disturbed and winds occur in excess of <br /> a threshold wind speed. Once the two conditions have been met, the emission factor is used to 1 <br /> determine how much dust is generated. No more wind erosion occurs until the surface is again <br /> disturbed and the wind again exceeds the threshold speed. For conservatism, the calculation <br /> assumes the storage piles will be disturbed daily and,therefore,N equals 366 disturbances per <br /> year. <br /> Based on available data,the emission factor for wind erosion activities is 5.25 pounds of PM10 <br /> per square meter of stockpile(uncontrolled)and 1.31 pounds per square meter of stockpile <br /> (controlled). Emissions were based on a continuously exposed stockpile area of 50 square <br /> meters. To account for emission controls,a control efficiency of 75% was applied. <br /> Unpaved Roads <br /> When a vehicle travels over an unpaved road,the force of the wheels on the road surface causes <br /> pulverization of surface material.Particles are lifted and dropped from the rolling wheels, and the <br /> road surface is exposed to strong air currents in turbulent shear with the surface. The turbulent <br /> wake behind the vehicle continues to act on the road surface after the vehicle has passed. The <br /> emission factors were calculated using the methodology found in Section 13.2 of AP-42, <br /> Unpaved Roads. The equation for developing the emission factor is: <br /> EF = k (S/12)a(W/3)b[(365-p)/3651 (1-CE) <br /> where: <br /> k (PMIO) = 1.5 (empirical constant) <br /> S = 10% (silt content) (use whole number value) <br /> W = 34 tons(mean vehicle weight,average of empty and full) <br /> p = 72(precipitation days) <br /> a = 0.9 (empirical constant) <br /> b = 0.45 (empirical constant) <br /> CE = 75% (empirical constant) <br />