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Usage of Open Path FTIR for the detection of toxic aerosols

Oz Kira, Ph.D. 

Airborne pesticides may pose a threat to public health. Monitoring airborne pesticides, in real time, has substantial importance when dealing with risk assessment. The information of pesticide drifts in semi-arid and arid climate, such as in Israel, is limited and thus further investigation is needed. In the present research we concentrate on measurements in the thermal infrared region using Open-Path Fourier Transform Infra-Red spectrophotometer (OP-FTIR). Infrared instruments have shown significant potential for detecting and identifying airborne compounds. However, up till now most studies using OP-FTIR were restricted to measuring gaseous components.

Remote sensing of a cloud of droplets relays significantly on the temperature difference between the background of the line of sight (LOS) and the surrounding environment. In order to test the OP-FTIR abilities to measure efficiently the clouds signature, which will allow achieving the two main research objectives of detection and quantification of the pesticide cloud, two main and different sites were chosen. The first, 20 meters long greenhouse, allows measurements of the pesticide cloud with minimal temperature difference between the background (soil) and the surrounding (polyethylene sheets), which are very limiting conditions, to test the system sensitivity.  The second site, a peach orchard, simulates a real field experiment with changing environmental conditions but with higher temperature contrast between the background (soil and trees) and the surrounding (sky).

The cloud's signal is extremely difficult to isolate duo to high background noise, caused by the ambient atmosphere and the background in the line of sight (LOS). Data analysis relies on chemometric tools and also on radiative transfer modeling of the obtained signals by combining inverse modeling with radiative transfer models and radiative transfer code – MODTRAN (MODerate resolution atmospheric TRANsmission).

The data provided by the measurements will be useful for calibrating and validating models of Aeolian transport and aerosolized pollutants.

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