Performance of Single Point Monitors for Measuring Aerial Ammonia and Hydrogen Sulfide

Performance of 43-44 Single Point Monitors (SPMs) was evaluated for measuring aerial ammonia (NH3, 0-30 ppm) and hydrogen sulfide (H2S, 0-90 ppb) under laboratory and field conditions. Calibration gas or sample air with various levels of moisture content or dew-point temperature (tdp) and gas concentrations were introduced simultaneously to the SPMs and a reference gas analyzer – chemiluminescence analyzer for NH3 and pulsed-fluorescence analyzer for H2S. Linear relationships were observed between readings of the SPMs and those of the respective reference analyzer, which were influenced by moisture content or tdp of the calibration or sample air. Specifically, average H2S readings by the SPMs were, respectively, 66%, 80%, 87% and 97% of those by the reference analyzer for calibration gas at tdp of -22 (dry), 9, 13 and 16 oC. In comparison, average NH3 readings by the SPMs were 42%, 86%, 102% and 178% of those by the reference analyzer for calibration gas at tdp of -22, 8.5-10, 12.5-14, and 16-17 oC respectively. Coefficient of variation of “as-is” readings among the tested SPMs was up to 15% for H2S and up to 25% for NH3. Regression equations were developed to compensate for the moisture effect on SPM readings of both gases. The correctional regression equations were able to achieve over 90% of the reference H2S readings; however, such equations were not as effective in predicting or correcting NH3 readings by the SPMs.