Infrared spectroscopic signatures of static aerosol panels

This report describes the infrared spectral characterization of stationary “static” aerosol test panels. These panels were designed to allow for a relatively simple test methodology for standoff optical detection of chemical aerosols. In a laboratory or field setting dynamic aerosols are challenging to generate and control with any precision and require significant times to prepare, calibrate and clean up before, during, and after a test release has been performed. In contrast to dynamic aerosols, static aerosol test panels offer reproducibility, rapid interchangeability, chemical diversity, and unambiguous quantification. We have fabricated test panels with particles, representing the aerosol, deposited on one surface of an infrared (IR) transparent substrate. Another identical bare substrate is brought near or in contact with the particle-coated surface, thereby helping to protect and contain the particle-coated surface. These panels are intended to represent a 3-dimensional aerosol cloud compressed along the beam propagation axis into a 2- dimensional rendering. Polished potassium bromide (KBr) plates and polyethylene membranes were chosen as substrates for this set of panels. Depending on the chemical selected and particle sizes desired, jet milling, sieving, and ultrasonic nebulization were used to fabricate the particle coated test panels to simulate aerosol clouds. In some instances, liquid chemicals were simply coated as a film on the IR transparent substrates. This simplification was found useful for chemicals which did not bead up suitably on the substrate utilized. The infrared spectral characterization of these panels indicates that they offer reproducible signatures representing a wide variety of chemicals, particle sizes, and concentrations.