Fumigants
129
FIGURE 8.4
Methods for determining emission losses of fumigants in the feld. For more on feld chambers,
the reader is referred to Yates (2006).
FIGURE 8.5
Flux feld designs showing options for placing air samplers for (a) the aerodynamic fux
method, (b) the integrated horizontal fux method, and (c) dispersion measurements.
scenarios through numeric techniques that correlate pesticide physicochemical properties with measured emissions (Woodrow et al., 2011).
To measure dispersion, single tiered masts are placed in downwind arrays
(Figure 8.5). However, these laborious dispersion assays can be replaced with
Gaussian plume dispersion models that use the measured emissions rate and
weather data to approximate downwind concentrations for exposure/risk
assessment (see Chapter 5) (Honaganahalli and Seiber, 2000; Woodrow et al.,
1997). These computer-based Gaussian plume dispersion models can also be
used to back-calculate a fux term when the downwind concentrations are
known, for comparison with measured fux (Seiber et al., 1996).
8.3.1 Flux from a Single Fallow Field
To illustrate, a feld study was conducted of MeBr volatilization fux, dispersion, and atmospheric fate in Monterey County, California, in 1994 (Seiber
et al., 1996). Flux, vertical profle, and single-height air concentrations were
measured at four different locations extending from the center of the treated
feld to nearly 0.8 km downwind (Figure 8.6). MeBr trapped on charcoal
129
FIGURE 8.4
Methods for determining emission losses of fumigants in the feld. For more on feld chambers,
the reader is referred to Yates (2006).
FIGURE 8.5
Flux feld designs showing options for placing air samplers for (a) the aerodynamic fux
method, (b) the integrated horizontal fux method, and (c) dispersion measurements.
scenarios through numeric techniques that correlate pesticide physicochemical properties with measured emissions (Woodrow et al., 2011).
To measure dispersion, single tiered masts are placed in downwind arrays
(Figure 8.5). However, these laborious dispersion assays can be replaced with
Gaussian plume dispersion models that use the measured emissions rate and
weather data to approximate downwind concentrations for exposure/risk
assessment (see Chapter 5) (Honaganahalli and Seiber, 2000; Woodrow et al.,
1997). These computer-based Gaussian plume dispersion models can also be
used to back-calculate a fux term when the downwind concentrations are
known, for comparison with measured fux (Seiber et al., 1996).
8.3.1 Flux from a Single Fallow Field
To illustrate, a feld study was conducted of MeBr volatilization fux, dispersion, and atmospheric fate in Monterey County, California, in 1994 (Seiber
et al., 1996). Flux, vertical profle, and single-height air concentrations were
measured at four different locations extending from the center of the treated
feld to nearly 0.8 km downwind (Figure 8.6). MeBr trapped on charcoal