Real time chemical vapor detection and enhancement utilizing aerosol adsorption

Abstract

A new trace gas detection system, using the high surface area properties of an aerosol to adsorb specific gas species and the high sensitivity and near real time capabilities of the infrared aerosol analyzer, has been successfully demonstrated. A new technique is described that allows certain chemical vapor species to be detected in time frames on the order of 2 min. The technique uses aerosols of selected materials to adsorb the vapor from an air sample, concentrating the vapor onto the surface of the aerosol, then depositing the particles onto a substrate for infrared analysis. For 1 min sample collection times, discernable signals were observed for SO2 levels as low as 2.3 ppm and NH3 concentrations as low as 1.5 ppm. Dimethyl methyl phosphonate (DMMP) vapors from a room temperature container were also detected. Preliminary results indicate that the measured absorbance is a monotonic function of the quantity of the trace gas injected, which gives encouraging evidence that a quantitative determination of the amounts of trace gases present in the atmosphere can be made in many cases. Trace gas detection is dependent upon the aerosol material chosen as the absorbent. For this work, copper (II) chloride and copper (II) sulfate were found to adsorb NH3, SO2, and DMMP. The copper compounds did not absorb NO or NO2. This enables the system to reduce the myriad potential interferences that can exist when sampling the atmosphere. The ammonia complex detected by this technique could be one of many such complexes that can be formed by properly matching the aerosol material and trace gas. As such, the process could be tailored to specific gas/aerosol combinations that could be used to unambiguously identify gaseous effluents of interest.