53:050
Natural Environmental Systems
Solutions to Homework No. 8 – Spring 2011
1.
Problem 62 in Davis and Masten.
First we have to convert ppm in gas to mg/m
3
using the ideal gas law (like previous HW!).
Assuming 1 atm total pressure (given), 10 ppm = 10 x 10
6
atm = 10
5
atm.
Also, recall that
the MW of H
2
S = 34.
The temperature is given as 25
o
C (= 298 K).
pV = nRT
V
n
=
RT
p
=
)
L/m
mg/mol)(10
000
,
34
(
K)
298
)(
K

mol
atm

L
(0.0821
atm
10
3
3
5
= 13.9 mg/m
3
Now we estimate CDI using Eq. 615 (a modification of Eq. 69) with the following values
taken from the problem and from Table 68:
CA = 13.9 mg/m
3
(from above)
IR = 11.3 m
3
/d = 0.471 m
3
/h (Table 68)
ET = 8 hours per event (from problem statement)
EF = 5 d/wk(50 wk/yr) = 250 events/yr (from problem statement)
ED = 65 yr old – 18 yr old = 47 yr (from problem statement)
BW = 65.4 kg (Table 68)
AT = 75 yr (EPA assumed lifetime (p. 232)
CDI =
d/yr)
yr)(365
kg)(75
(65.4
yr)
(47
events/yr)
50
h/event)(2
/h)(8
m
)(0.471
mg/m
(13.9
3
3
CDI = 0.344 mg/kgd
2.
Problem 65 in Davis and Masten.
Compare adult and child CDI for 2,4D.
Using Table 68 values for 3year old child:
CDI =
yr)
wk/yr)(1
d/wk)(20
kg)(1
(16
yr)
wk/yr)(1
d/wk)(20
)(1
kg/mg)(0.1
mg/d)(10
mg/kg)(100
(10
6
CDI
child
= 6.25 x 10
6
mg/kgd
Using Table 68 for an adult:
CDI =
yr)
wk/yr)(1
d/wk)(20
kg)(1
(78
yr)
wk/yr)(1
d/wk)(20
)(1
kg/mg)(0.1
mg/d)(10
mg/kg)(50
(10
6
CDI
adult
= 6.41 x 10
7
mg/kgd
1
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Problem 67 in Davis and Masten.
Here we will be calculating cumulative CDI from (1)
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 Spring '11
 Parkin
 Trigraph, Yr

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