Submitted to: Applied Engineering in Agriculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2004
Publication Date: 11/1/2004
Citation: Liang, Y., Xin, H., Hoff, S.J., Richard, T.L., Kerr, B.J. 2004. Performance of single point monitors in measuring ammonia and hydrogen sulfide gases. Applied Engineering in Agriculture. 20:863-872. Interpretive Summary: Air pollutants, such as ammonia, nitrous oxide, methane, hydrogen sulfide, carbon dioxide, and particulate matter are generally associated with animal feeding operations. Ammonia and hydrogen sulfide have received particular attention due to their potential health effects. As the need to determine gas concentrations and emission rates increases, various measurement methods and instruments have evolved. Single point monitors are one of these instruments that have been used to monitor ammonia and hydrogen sulfide levels in or around swine production facilities. Single point monitors measure gas levels based on the rate of color change of a chemical cassette tape that reacts with the target gas. The odor intensity change of the tape is sensed by a photocell whose output is then converted to analog output and digital display of the gas level. The advantages of a single point monitor include its relatively low cost, portability for field application, and its ability to detect relatively low gas concentrations. The major drawbacks and concerns include their large uncertainty in measuring the 'true' concentration, susceptibility to measurement interference by moisture content in the air sample, and inability of field or user calibration. Experimentation indicated that: 1) single point monitors show weak interchangeability, especially for ammonia, thus individual monitor calibration and correction is recommended, 2) moisture content in the sample air elevates gas concentration readings by single point monitor units such that concurrent knowledge of moisture content in the air sample is necessary to compensate for the moisture interference, and 3) while the moisture interference on single point monitor measurements can be mathematically compensated for hydrogen sulfide gas, achieving 97% agreement with the reference value, this compensation was not as effective for ammonia measurements. As environmental issues from livestock operations become more pressing and regulatory standards are set, it is critical that instruments used in setting and enforcing these standards are accurate in their analysis of ammonia and hydrogen sulfide concentrations. Research results described in this report provide scientists at universities and regulatory agencies vital data on the variability and reliability of single point monitors in measuring concentrations of ammonia and hydrogen sulfide around livestock production facilities.
Technical Abstract: Performance of Single Point Monitors was evaluated for measuring aerial ammonia (0-30 ppm) and hydrogen sulfide (0-90 ppb) under laboratory and field conditions. Calibration gas or sample air with various levels of moisture content or dew-point temperature and gas concentrations at a dry-bulb temperature of 24.4 ºC were introduced simultaneously to the Single Point Monitors and a reference gas analyzer - chemiluminescence analyzer for ammonia and pulsed-fluorescence analyzer for hydrogen sulfide. Linear relationships were observed between readings of the Single Point Monitors and those of the respective reference analyzer, which were influenced by moisture content or dew-point temperature of the calibration or sample air. Specifically, average hydrogen sulfide readings by the Single Point Monitors were, respectively, 66%, 80%, 87% and 97% of those by the reference analyzer for calibration gas at dew-point temperature of -22 (dry), 9, 13 and 16 ºC (-7.6, 48, 55 and 61 ºF). In comparison, average ammonia readings by the Single Point Monitors were 42%, 86%, 102% and 178% of those by the reference analyzer for calibration gas at dew-point temperature of -22, 8.5-10, 12.5-14, and 16-17 ºC (-7.6, 47-50, 55-57 and 61-63 ºF), respectively. Coefficients of variation of 'as-is' readings among the tested Single Point Monitors were up to 15% for hydrogen sulfide and up to 25% for ammonia. Regression equations were developed to compensate for the moisture effect on Single Point Monitor readings of both gases. The correctional regression equations were able to achieve over 90% of the reference hydrogen sulfide readings; however, such equations were not as effective in predicting or correcting ammonia readings by the Single Point Monitors.