Aircraft Measurements of the Concentration and Flux of Agrochemicals

Abstract

The use of agrochemicals, such as insecticides and herbicides, is of great environmental concern. To quantify and model the volatilization and deposition of these agrochemicals, measurements of the exchange rates between the atmosphere and different surfaces are required. An aircraft-based air sampling system using the relaxed eddy-accumulation technique for measuring concentrations and fluxes of agrochemicals was developed and tested in June 1993 and July 1994. Atrazine and metolachlor, which are used on corn and soybean crops, were detected in samples collected along flights from Ottawa to southern Ontario. Concentrations as high as 4.6 ng m-3 for atrazine and 9.8 ng m-3 for metolachlor were found. Fluxes ranged from −1.1 to 2.5 ng m-2 s-1 for atrazine and from −0.01 to 0.56 ng m-2 s-1 for metolachlor. These results demonstrate that the aircraft-based relaxed eddy-accumulation ap proach is a useful method for measuring concentrations and fluxes of agrochemicals at both local and regional scales. Combined with footprint calculations and air mass back-trajectories methods, the fluxes measured with this system should be useful to improve our understanding of the long-range transport of semivolatile organic compounds and their potential impact on various ecosystems.