Quantitation of hydrogen sulfide reference gas mixtures to provide traceability for indoor air quality monitoring

Accurate measurements for the determination of hydrogen sulfide (H₂S) are critical for the compliance with legislation in various industries, including natural gas and environmental sectors such as air pollution monitoring. H₂S measurements at ambient level are challenging because H₂S tends to adsorb on the internal surfaces of the sample collection devices such as gas cylinders and transfer lines. Prolonged exposure to H₂S has known health implications to humans, such as irritation to the nose, throat and airways that results in coughing or inflammation, wheezing and shortness of breath around the chest. H₂S is mainly monitored for occupational health and safety and indoor air quality monitoring. It is a highly reactive gas that can easily react with oxygen to form sulfur dioxide (SO₂) and with water to form sulfuric acid (H₂SO₄). The traceability of H₂S measurements is achieved through the preparation of reference gas mixtures. These gas mixtures are gravimetrically prepared in accordance with International Organization for Standardization (ISO 6142–1:2015). The H₂S reference gas mixtures were produced with the highest metrological capability; thus, the molar mass, purity assessment, and the weighing gave an overall gravimetric relative uncertainty which is less than 0.10% (k?=?1). One of the biggest challenges in producing a H₂S reference gas mixture is the handling of a gas cylinder from the gravimetric preparation process until the verification stage. This work will detail the improved techniques and measurements used to produce the H₂S reference gas mixtures. The internal consistency between the mixtures was verified using a non-dispersive ultraviolet (NDUV) spectroscopy analyzer, an ultraviolet fluorescence spectroscopy (UVFS) analyzer and gas chromatography coupled with a pulsed discharged helium ionization detector (GC-PDHID). Our measurement uncertainty results show that the gravimetric value, internal consistency, adsorption, homogeneity, and stability were within a relative uncertainty of 1.2% as compared to our previous uncertainty of 4.4%. This is a significant improvement for the measurements of H₂S reference gas mixtures.