Human Health Risk Assessment - Raytheon

u = Wind speed (m/s)
23
Human Health Risk Assessment
DRAFT
The air/water partition coefficient used in this model is the dimensionless Henry’s Law constant,
which varies with temperature, and is calculated according to equation (4-9).
where:
K eq
H = Henry’s Law constant (atm-m 3 /mole)
H
= (4-9)
R ⋅ T
R = Ideal gas constant (8.206 x 10 -5 atm-m 3 /mole-K)
T = Temperature in degrees Kelvin (K)
The gas phase mass transfer coefficient in units of meters per second can be estimated from
equation (4-10) based on the work of Mackay and Matsugu (1973) 7 .
where:
Scg = Schmidt number
g
−3
0.
78 −0.
67 −0.
11
= 4.
82x10
⋅ u ⋅ ScG
⋅ d e
k (4-10)
de = Effective diameter of the area emitting
The Schmidt number is a dimensionless number that relates to the relative thickness of the
surface boundary layer and is calculated according to equation (4-11).
where:
Sc
g
µ g
=
ρ ⋅ D
µg = Viscosity of air (1.81 x 10 -4 g/cm-s)
ρg = Density of air (1.2 x 10 -3 g/cm 3 )
Da = Diffusivity of COPC in air (cm 2 /s)
The emission rate calculated from equation (4-6) is combined with the box model described by
equation (4-3) to arrive at an upper bound estimate of outdoor air concentrations in the vicinity
g
a
(4-11)
7 D. Mackay and R.S. Matsugu. 1973. Evaporation rates of liquid hydrocarbon spills on land and water. Canadian J.
Chem Eng. 51:434.