Conductometric Sensor for Parts per Billion Sulfur Dioxide Determination

A conductometric sensor for the determination of atmospheric sulfur dioxide levels is described. It consists of a hydrophobic, gas-porous membrane that separates the gas sample from a thin film of pure water. Sulfur dioxide from the gas phase diffuses through the membrane and rapidly equilibrates In the water layer. Conductivity electrodes positioned within the thin layer measure Its conductance. The theory relating the square of the equilibrium conductance to the partial pressure of sulfur dioxide is given. The behavior of the sensor to sulfur dioxide Is characterized and contrasted to that of carbon dioxide. Linear calibration curves were obtained over a range of 20–1000 ppb SO₂. Response times were on the order of 90–120 s.