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United States Department of Agriculture

Agricultural Research Service

Title: Vapor-Particle Partitioning of Metolachlor and Atrazine: Deviation from Model Predictions

Authors
item McConnell, Laura
item Torrents, Alba - UNIV. OF MARYLAND
item Kuang, Z. - UNIV. OF MARYLAND
item Harman Fetcho, Jennifer

Submitted to: Society of Environmental Toxicology and Chemistry Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: November 17, 2002
Publication Date: N/A

Technical Abstract: The environmental fate of airborne organic pollutants, i.e., atmospheric lifetime, is often governed by their distribution between the vapor and particle phases. An accurate understanding of the chemical-specific air-particle interactions is necessary to predict the distance a particular chemical may travel from its source and the loadings it may contribute to non-target regions. Air samples were collected in two different agricultural watersheds within the larger Chesapeake Bay system. This project is an examination of atrazine and metolachlor with respect to trends in concentration, vapor-particle distribution, and a comparison of observed vs. predicted particle-phase fractions (F) using the Junge-Pankow and Octanol-Air approaches. In a comparison of F(pred) and F(obs) over time, observed values were approximately 1.4-15 and 0.67-53 times as high as predicted values for atrazine and metolachlor, respectively, indicating that the model underestimates the sorption of these polar chemicals to aerosols. Alternatively, this may indicate that atrazine and metolachlor are not at equilibrium in the atmosphere. Further examination of the data revealed that deviation from model predictions was largest during the spring and early summer when the chemicals were applied. For instance, in late spring and in the summer, the ratio of obs/pred for metalochlor ranged from 3.1 to 53 compared with 0.9-1.5 in April and 0.67-2.0 in November and December. A similar trend was also found for atrazine, where the ratio of obs/pred was 4.1 -15 from May to July compared with 2.0-2.8 in April and 1.5-1.8 in winter.

Last Modified: 7/27/2014
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