Real time chemical vapor detection and enhancement utilizing aerosol adsorption

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 nea r real time capabilities of the infrared aerosol analyzer, has been success fully demonstrated. A new technique is described that allows certain chemic al vapor species to be detected in time frames on the order of 2 min. The t echnique uses aerosols of selected materials to adsorb the vapor from an ai r sample, concentrating the vapor onto the surface of the aerosol, then dep ositing the particles onto a substrate for infrared analysis. For 1 min sam ple collection times, discernable signals were observed for SO2 levels as l ow as 2.3 ppm and NH3 concentrations as low as 1.5 ppm. Dimethyl methyl pho sphonate (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 p resent 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 sa mpling 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 s pecific gas/aerosol combinations that could be used to unambiguously identi fy gaseous effluents of interest. (C) 1999 American Institute of Physics. [ S0034-6748(99)03003-8].