Correlated Transmission and Detection of Concentration-Modulated Chemical Vapor Plumes

We present an experimental system designed to explore vapor propagation and detection limits with temporally correlated chemical plumes. By introducing a non-random temporal structure into a chemical source, we can apply correlated detection to statistically identify unique concentration-modulated patterns over meter-scale distances, at frequencies up to 100 Hz, and at concentrations at least two orders of magnitude below the nominal limit of detection of a given sensor. As an illustration of these concepts, we detect 1 ppb modulated isopropanol vapor in a >1 ppm ambient volatile organic compound background, using non-selective photoionization detectors having a nominal sensitivity of approximately 100 ppb. We aim to extend these concepts more broadly to improve the sensitivity and reliability of low-cost chemical sensor networks.