Effect of emission source intensity was also examined. For primary
drift, source intensity was varied between 1%, 10% and 30% of
total pesticide applied. For the 1% scenario, elevated (>1 mg m3
)
pesticide concentrations were obtained only over the treated field,
and did not exceed 0.25 mg m3
. Very similar dispersion patterns
were calculated for emissions of 10% (Fig. 3a) and 30%, with higher
air concentrations for the latter. For secondary drift emission rates
were calculated based on first order evaporation kinetic, with
evaporation rate constants of k ¼ 0.05, 0.015 and 0.005 hour1
(primary drift was 10%). As expected, reducing the emission rate
reduces the calculated air concentrations. This was most noteworthy
in the second-night after application (data not shown). It is
worth noting that for the whole simulation duration, i.e. 2 days
after application, calculated air concentrations were above the
Texas ESL in the orchard vicinity, indicating the need for more
temporal and spatial air sampling data.
4