Optoacoustic detection of ethylene in the presence of interfering gases

Abstract

A study of the limitations of optoacoustic detection of ethylene in gas mixtures using a ¹²C¹⁶O₂ laser is presented. Particular emphasis is given to the detection of ethylene in urban areas and in fruit storage chambers. Calculations indicate that in most cases of interest the practical minimum detectable and identifiable concentration of ethylene is about 5 ppb. A concentration of 1% of CO₂ may increase this limit to 50 ppb. These limits are primarily due to inaccuracy in a priori knowledge of ir spectral signatures of interfering gases. As a practical example of the monitoring of ethylene in a realistic environment, a meausrement with a sensitive resonant optoacoustic cell in an urban area is reported. The same cell is also used to demonstrate the effectiveness of NaOH scrubbers for the elimination of interfering CO₂. Measurements of absorption coefficients of ethylene for several ¹²C¹⁶O₂ laser transitions are reported and compared with those given in the literature. Data are also given for the isotopic ¹³C¹⁶O₂ laser transitions which may be useful in overcoming CO₂ interference.