|M.Sc Student||Arnon Adva|
|Subject||Using Open Path FTIR for Real Time Monitoring of|
Aerosolized Pesticide Drift
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Yael Dubowski|
|Professor Raphael Linker|
|Full Thesis text|
Spray drift is a major pollution source following pesticides applications. The current research examines the potential of Open-Path Fourier Transform Infrared (OP-FTIR) spectroscopy as an alternative method for near real-time monitoring of spray drift from orchard under field conditions.
The general aim of the study was to evaluate the ability of active OP-FTIR to identify and quantify airborne pesticide spray-drift and other fine aerosols. This is a challenging analytical goal, since FTIR technique is based on infrared absorption features, whereas aerosols also scatter this radiation very efficiently.
The experimental work included two main parts: spray tunnel experiments and field measurements. Initial spray-tunnel experiments focused on detection of fine organic aerosol cloud (~300 nm) generated using a smoke machine. In line with Beer-Lambert law, a good linear regression was obtained between measured OP-FTIR extinction spectra and aerosols concentration (measured with an aerosol counter). Second stage of spray tunnel work involved water spray from a typical agricultural pesticide spraying system. Five nozzles generating droplets ranging from 60 to 215 microns were tested. According to Mie-theory, the interaction between infrared light and droplets of few microns results in a significant component of scattered light. The OP-FTIR system clearly detected the spray clouds and could distinguish between the various clouds in terms of droplet sizes. For quantification, size distributions of droplets were measured using a Spraytec system, and a model based on Mie scattering calculated the expected extinction spectra. The disparity between the measured and calculated spectra suggested that the size distribution data was not accurate enough. Still, it was discovered that the number size distribution of all five nozzles are similar and the main difference between them is in the water load.
The second part of the study consisted on measurements during agricultural pesticide application in a peach orchard. Six tree rows were sprayed. The spectrometer, located at the edge of the orchard, was measuring continuously before, during and after application. Drift that resulted from spraying the five rows closest to the OP-FTIR was clearly detected, with increasing signal intensity when moving closer to spectrometer. Spectra also suggest drift reduction due to tree-line barrier.
To conclude, OP-FTIR was found to be a reliable tool for detecting airborne pesticide spray-drift and other fine aerosols. This study demonstrated that due to its high sensitivity and near real-time monitoring abilities, OP-FTIR has the potential to become an alternative tool for measuring pesticide drift at the field.