Pesticides have been found in outdoor air samples. Where do they come from? They could be originating from local, regional or global sources. Locally, pesticide drift may be a factor. Pesticide drift is when pesticides unintentionally move from the application site. Drift is more likely to occur with fumigants (gasses), dusts or when liquid pesticides are applied as a very fine mist. Drift is also more likely to occur on windy days and when temperatures are very high.

In addition to pesticides released locally, pesticides in the air can rise to very high altitudes and move for long distances attached to particles. Scientists have found particles released in the atmosphere from Europe and Asia in forests on the U.S. west coast. Particles traveling across the United States from the Midwest to the east coast to the Atlantic Ocean and Europe travel in what is called a boundary layer. The Gulf Stream can transport particles from Florida to Maine. These particles can enter our ecosystem when they are deposited as rain or snow.