EPA Accepts NAAA’s Recommendations to Improve Accuracy of Aerial Drift Model

After years of effort, the EPA has finally accepted NAAA’s recommendations to improve the accuracy of the models used to estimate the amount of drift from aerial applications. Until the recently released Insecticide Strategy (IS) (see article below), EPA had used the Tier 1 model in AgDRIFT, which had many erroneous and outdated assumptions, including the typical droplet size used, aircraft type reflecting the industry, weather conditions during the application, and boom drop.

This resulted in unrealistic aerial drift estimates, which in turn were used in environmental and human health risk assessments. The result has been decades of pesticide registration risk assessments and decisions that have overstated the risk aerial application presents to our environment and fellow citizens. In the IS, EPA used the Tier 3 model in AgDRIFT and most of NAAA’s suggested assumptions for the variables within the model. NAAA submitted a letter to EPA in June of 2020 outlining recommended changes in the assumptions that should be used in the Tier 3 AgDRIFT model. Prior to that letter, NAAA has included the recommendations on numerous comments to EPA.

EPA changed the default aircraft from an AT-401 to an AT-802 with a corresponding increase in swath width and decrease in the number of passes. The default droplet size was increased to medium, and the atmospheric stability was set to a level that rules out the presence of an inversion. EPA also changed the height at which wind speed is measured to reflect smokers and onboard meteorological measurement systems and increased the upwind swath displacement to reflect what is actually practiced in the industry.

There were two assumptions EPA did not agree with completely on with NAAA – surface roughness and standard boom drop. While EPA did not agree with the values proposed by NAAA, they did not disagree with the logic behind our recommendations. NAAA will conduct additional data collection and analysis to better support our positions in a future follow up letter to EPA on these two variables.

With EPA’s change to the Tier 3 model, the estimated drift from aerial applications has been substantially reduced. This will make it far easier for pesticide registrants to label their products for aerial applications, ensuring ag aviation industry’s customers can continue to rely on the aerial application of products to protect their crops.

This is a major example of what NAAA does for the aerial application industry—ensuring the availability of pesticides without unnecessary or burdensome restrictions.  It takes resources to accomplish this.  It takes membership so if you don’t currently belong to NAAA please click here to join.