Environmental Engineering Reference
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transformed with only 4% remaining. Concentrations of CPY would be
approximately 0.005 ng m −3 (0.035 nPa). Approximately 70% of the concentrations
measured in air are in the range of 0.01-1.0 ng CPY m −3 and probably correspond
to distances from sources of 30-200 km. Predicted concentrations in rain at steady
state would be 0.02-2.0 ng CPY L 1 and those in snow would be 0.3-30 ng CPY L −1 ,
with some 39% of the reported concentrations in snow being in this range. Most of
these data are restricted to one region, the Sierra Nevada Mountains in the U.S.
Predicted fugacities and concentrations in snow are speculative since the air/snow
partition coefficient is uncertain and concentrations are undoubtedly influenced by
timing of the snowfall relative to applications. Heavier snowfall, such as occurs in
the Sierra Nevada might result in dilution in the precipitation and near-total scav-
enging of CPY from the atmosphere.
At a distance of 300 km and about 20 h transit time, which is equivalent to
approximately five CTDs, 1.0% of the initial mass of CPY would remain because
the CPY would have been subjected to nearly 7 half-lives. Concentrations at this
distance from the source would likely be 0.0003 ng CPY m −3 (0.002 nPa) or less.
Concentrations of 0.003 ng CPYO m −3 would be expected. Thus, at this distance
from the source, CPYO would be the primary product present, at a concentration
which is near the typical limit of quantitation. Rain, if at equilibrium with air, would
be expected to contain a concentration of 0.001 ng CPY L −1 and snow 0.02 ng CPY
L −1 . Given an assumed half-life of 3 h and the time to be transported this distance, it
is unlikely that, under normal conditions, significant quantities could travel more
than 300 km. Observations of detectable amounts of CPY at greater distances, such
as 1,000 km, suggest that, at least under certain conditions, the half-life is longer
than was assumed in this analysis. For example, significant concentrations of CPY
have been measured in the Svalbard ice-cap (Hermanson et al. 2005 ). It is likely that
these residues originated from Russia and were transported at times of lesser tem-
peratures, greater wind speeds, and limited photolysis, which results in a longer
CTD of the order of 300-1,000 km. Concentrations of CPY measured by Muir et al.
( 2004 ) in arctic lakes might also reflect slow transformation in the presence of
smallerconcentrationsof•OHatthesehigherlatitudes.
Monitoring data and the tentative modeling described here indicate that CPY and
CPYO are detectable in air at concentrations exceeding 0.1 ng m −3 at distances of up
to 60 km from the source and at 0.01 ng m −3 at distances up to 200 km, except in the
Sierra Nevada where there are meteorological constraints on flows of air masses.
There will be corresponding concentrations in rain, snow, and in terrestrial media
such as pine needles and biota. There is an incentive to monitor these media because
of the greater concentrations and increased analytical reliability. The “zone of
potential influence” of LRT in this case is one to two CTDs or up to 60-120 km
from the point of application. Reactivities of CPY and CPYO are such that concerns
about LRT are much more localized than for organochlorines, which are more per-
sistent and thus might have CTDs of thousands of km. The results of the analysis
presented here suggest that it is feasible to extend assessments of LRT beyond the
mere estimation of CTD and CTT to address the magnitude of the concentrations
and fugacities along a typical LRT transect and to estimate absolute multi-media
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