Water vapor inhibits hydrogen sulfide detection in pulsed fluorescence sulfur monitors

The Thermo Scientific 450 Hydrogen Sulfide–Sulfur Dioxide Analyzer measures both hydrogen sulfide (H₂S) and sulfur dioxide (SO₂). Sulfur dioxide is measured by pulsed fluorescence, while H₂S is converted to SO₂ with a molybdenum catalyst prior to detection. The 450 is widely used to measure ambient concentrations, e.g., for emissions monitoring and pollution control. An air stream with a constant H₂S concentration was generated and the output of the analyzer recorded as a function of relative humidity (RH). The analyzer underreported H₂S as soon as the relative humidity was increased. The fraction of undetected H₂S increased from 8.3 at 5.3 % RH (294 K) to over 34 % at RH  >  80 %. Hydrogen sulfide mole fractions of 573, 1142, and 5145 ppb were tested. The findings indicate that previous results obtained with instruments using similar catalysts should be re-evaluated to correct for interference from water vapor. It is suspected that water decreases the efficiency of the converter unit and thereby reduces the measured H₂S concentration

Dip coating of air purifier ceramic honeycombs with photocatalytic TiO₂nanoparticles: A case study for occupational exposure

Nanoscale TiO2 (nTiO2) is manufactured in high volumes and is of potential concern in occupational health. Here, we measured workers exposure levels while ceramic honeycombs were dip coated with liquid photoactive nanoparticle suspension and dried with an air blade. The measured nTiO2 concentration levels were used to assess process specific emission rates using a convolution theorem and to calculate inhalation dose rates of deposited nTiO2 particles. Dip coating did not result in detectable release of particles but air blade drying released fine-sized TiO2 and nTiO2 particles. nTiO2 was found in pure nTiO2 agglomerates and as individual particles deposited onto background particles. Total particle emission rates were 420 × 109 min−1, 1.33 × 109 μm2 min−1, and 3.5 mg min−1 respirable mass. During a continued repeated process, the average exposure level was 2.5 × 104 cm−3, 30.3 μm2 cm−3, <116 μg m−3 for particulate matter. The TiO2 average exposure level was 4.2 μg m−3, which is well below the maximum recommended exposure limit of 300 μg m−3 for nTiO2 proposed by the US National Institute for Occupational Safety and Health. During an 8-hour exposure, the observed concentrations would result in a lung deposited surface area of 4.3 × 10−3 cm2 g−1 of lung tissue and 13 μg of TiO2 to the trachea-bronchi, and alveolar regions. The dose levels were well below the one hundredth of the no observed effect level (NOEL1/100) of 0.11 cm2 g−1 for granular biodurable particles and a daily no significant risk dose level of 44 μg day−1. These emission rates can be used in a mass flow model to predict the impact of process emissions on personal and environmental exposure level