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SOIL-TO-AIR VOLATILIZATION FACTOR (VF,) <br /> Equation 4-9: Derivation of the Volatilization Factor <br /> (3 . 14 X DA X T) 1/2 X 10-6 (m2/cm2) <br /> VFB{m /kg) _ (010 X (2 X Pb x DA) <br /> where: <br /> (6;a/3DSHi + 6;,°/a D„) /n2j <br /> DA PaKd + 6y + 6sH� <br /> Parameter Definition (units). Default <br /> VF, Volatilization factor (m'/kg) — <br /> pA Apparent diffusivity (cm2/s) <br /> O/C Inverse of the mean conc. at the center of a 66.81 <br /> 0.5-acre square source (g/m2-s per kg/m') <br /> T Exposure interval (s) 9.5 x 10" <br /> Pe <br /> Dry soil bulk density (9/cm) 1.5 <br /> p• Alr filled soil porosity (L„JL aj 0.28 or n-O,, <br /> nTotal soil porosity (L,,,,/L.) 0.43 or 1 - (p,/pJ <br /> E). Water-filled soil porosity (Lw,,JL,,J 0.15 <br /> P. <br /> Soil particle density (9/cm) 2.65 <br /> pl Diffusivity in air (cm2/s) Chemical-specific <br /> H Henry's Law constant (atm-m'lmol) Chemical-specific <br /> H Dimensionless Henry's Law constant Calculated from H by multiplying <br /> by 41 (USEPA 1991a) <br /> DDiffusivity in water (cm2/s) Chemical-specific <br /> w <br /> K Solt-water partition coefficient (cm'/g) K„fa Chemical-specific <br /> e <br /> Ka Soil organic carbon-water partition coefficient (cm'/g) Chemical-specific <br /> f Fraction organic carbon in soil (g/g) 0.006 (0.6%) <br /> 19 <br />