Which of the following is not a method by which pesticides break down after application?

Pesticides break down through various processes after they are applied to the environment. Microbial degradation involves the action of microorganisms that metabolize the chemicals, breaking them down into less harmful substances. Photodegradation occurs when pesticides are decomposed by sunlight and UV radiation, leading to their transformation into simpler compounds.

Chemical degradation refers to the breaking down of pesticides through chemical reactions, often involving hydrolysis or oxidation, which can occur in the presence of water or air.

Atmospheric degradation, while the term may seem related to the breakdown of pesticides, is not generally recognized as a standard method of pesticide degradation. The term could be interpreted ambiguously, as it may suggest the effects of atmospheric conditions, but it does not specifically describe a recognized degradation process like the other options do. Thus, the choice regarding atmospheric degradation stands apart from the established mechanisms for pesticide breakdown.