Influence of clouds on the photochemical degradation in aqueous phase - II: Field measurements in Brazil and Germany

The photolysis of pesticides in aqueous solution is one of the key parameters used
assess their persistence in the environment. However:
III Photolysis lifetimes at different latitudes are obtained from quantum yields and UV
spectra in the laboratory together with calculated sunlight intensities. Comparison of
experimentally determined photolysis rates at different latitudes and under different
climatic conditions for pesticides has seldom been performed.
III Photolysis lifetimes of pesticides at different latitudes are usually calculated at noon
for summer months and have to be regarded as progressive values. Hence, the
influence of cloud cover on the photolysis is often neglected or not known.
We discuss on the poster:
III the comparison of the photolysis at two differing sites in the northern part of
Germany (LOneburg) and the southern part of Brazil (Santa Maria) with respect to
climate and sunlight intensity,
• diurnal variations of the photolysis reaction were in the focus of the measurement
performed with the herbicide metamitron (properties of metamitron are discussed
on an accompanying poster),
• an attempt to explain the photolysis-rate constants using a well established model
(STARsci) especially considering the influence of clouds,
• an assessment of the deviation of the "clear-sky" scenario often used for pesticides
and the influence of effective sun-light intensities influenced by clouds.