Environmental Engineering Reference
In-Depth Information
Fig. 2
Mass balance output from the TAPL3 LRT model. A 3 h half life is assumed for atmo-
spheric degradation. The CTD is 62 km. Other parameters are as specified in Tables
5
and
6
and
include the upper range (conservative) of half lives in water, soil and sediment in Table
6
. The
model can be downloaded from
www.trentu.ca/cemc
known, that rate must equal the net rate of loss from air. Dividing the calculated
mass in air by this rate gives the characteristic time defined above and this can be
converted to a distance by multiplying by the wind velocity
U
, which is convention-
ally assumed to be 14.4 km h
−1
or 4 m s
−1
. Alternatively, the residence time or char-
acteristic travel time (CTT) in air can be calculated as the mass in air divided by the
rate of emission. This approach is used in the TAPL3 model (Beyer et al.
2000
) and
in the similar OECD Tool described by Wegmann et al. (
2009
)
The output of the TAPL3 simulation model is given diagrammatically for the
selected half-life in air of 3.0 h (Fig.
2
) and includes the conservative (long) half
lives in other media (Table
7
). The mass in air is 4,328 kg and the emission rate to
air is 1,000 kg/h, thus, the residence time in air and the CTT is 4.3 h and the cor-
responding rate constant for total loss is 0.231 h
−1
. The CTD is approximately
62 km, which is the product of 4.3 h and the wind velocity of 14.4 km h
−1
. The rate
of transformation is 993 kg h
−1
and the net losses by deposition to water, vegeta-
tion, and soil total about 7 kg CPY h
−1
, which corresponds to a rate constant of
0.0016 h
−1
, and is less than 1% of the rate of degradation. The critical determinant
ofpotentialforLRTistherateoftransformationfromreactionswith•OHradicals
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