Hazardous gas detection using an integrating sphere as a multipass gas absorption cell

This paper describes a novel multipass gas absorption cell based on a spherical absorption cavity. An integrating sphere has been modified to allow the input and output of gas. Measurements have been performed using two hazardous gases: nitrogen dioxide and sulphur dioxide. Nitrogen dioxide is detected in the ultraviolet/visible region at 403 nm and sulphur dioxide in the ultraviolet region at 286 nm. The absorption spectrum of both gases is detected using a broadband deuterium halogen light source as an emitter and a spectrometer as a detector. Nitrogen dioxide concentration is measured using an ultraviolet LED as the emitter and photodiode as a detector. It is reported in this work that trace amounts of nitrogen dioxide (<5 parts per million, ppm) and sulphur dioxide (<15 ppm) can be detected using this sensor. A method of calculating the effective optical path length of the sensor is also presented.