Detection of SO₂F₂ Using a Photoacoustic Two-Chamber Approach

The wide use of sulfuryl difluoride (SO₂F₂) for termite control in buildings, warehouses and shipping containers requires the implementation of suitable sensors for reliable detection. SO₂F₂ is highly toxic to humans and the environment, and moreover, it is a potent greenhouse gas. We developed two photoacoustic two-chamber sensors with the aim to detect two different concentration ranges, 0-1 vol.-% SO₂F₂ and 0-100 ppm SO₂F₂, so that different applications can be targeted: the sensor for high concentrations for the effective treatment of buildings, containers, etc., and the sensor for low concentrations as personal safety device. Photoacoustic detectors were designed, fabricated, and then filled with either pure SO₂F₂ or pure substituent gas, the refrigerant R227ea, to detect SO₂F₂. Absorption cells with optical path lengths of 50 mm and 1.6 m were built for both concentration ranges. The sensitivity to SO₂F₂ as well as cross-sensitivities to CO₂ and H₂O were measured. The results show that concentrations below 1 ppm SO₂F₂ can be reliably detected, and possible cross-sensitivities can be effectively compensated.