National Water-Quality Assessment (NAWQA) Project
Pesticide National Synthesis Project
Pesticides in the Atmosphere
U.S. Geological Survey, Fact Sheet FS-152-95
Seasonality of Pesticides in Air and Rain
Locally high concentrations of pesticides in rain and air are
very seasonal and are correlated to local use. The highest
concentrations in air and rain usually occur in the spring and summer
months (see Figure 7), coinciding with application times
and warmer temperatures. However, insecticide concentrations
in air, rain, and fog can also be high during autumn and winter in
some areas, if there is high use at that time. This occurs in
California where stone-fruit orchards are sprayed for insects when
trees are dormant.
Figure 7. Average concentration of atrazine and alachlor in rain sampled in
the vicinity of Wye River, Maryland (Glotfelty and others, 1990).
Pesticides have also been detected at low levels during periods
before and substantially after use, but determining the
sources has proven difficult. These off-season occurrences could
be due to volatilization and wind erosion of previously applied
material, or the result of long-range transport from areas where
the growing season started earlier.
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