Estimation of the Interference in Multi-Gas Measurements Using Infrared Photoacoustic Analyzers

Abstract

Two methods were described to estimate interference in the measurements of infrared (IR) photoacoustic multi-gas analyzer (PAMGA). One is IR spectroscopic analysis (IRSA) and the other is mathematical simulation. An Innova 1412 analyzer (AirTech Instruments, Ballerup, Denmark) with two different filter configurations was used to provide examples that demonstrate the two methods. The filter configuration in Example #1 consists of methane (CH 4 ), methanol (MeOH), ethanol (EtOH), nitrous oxide (N 2 O), carbon dioxide (CO 2 ), and water vapor (H 2 O), and in Example #2 of ammonia (NH 3 ), MeOH, EtOH, N 2 O, CO 2 , and H 2 O. The interferences of NH 3 as a non-target gas in Example #1 were measured to validate the two methods. The interferences of H 2 O and NH 3 as target gases in Example #2 were also measured to evaluate the analyzer's internal cross compensation algorithm. Both simulation and experimental results showed that the interference between the target gases could be eliminated by the internal cross compensation algorithm. But the interferences of non-target gases on target gases could not be addressed by the internal cross compensation, while they could be assessed by the IRSA and mathematical simulation methods. If the IR spectrum of a non-target gas overlaps with that of target gas A at filter A, it could affect not only gas A (primary interference), but OPEN ACCESSAtmosphere 2012, 3 247 also other target gases by secondary interference (because the IR spectrum of gas A overlaps with gas B at filter B and thus affects gas B measurements). The IRSA and mathematical simulation methods can be used to estimate the interference in IR PAMGA measurements prior to purchase or calibration of the unit.

Methane and nitrous oxide analyzer comparison and emissions from dairy freestall barns with manure flushing and scraping

“…When selecting an analyzer for greenhouse gas measurements, recommended practices are to evaluate the analyzer's recommended range, and conduct pilot tests to assure that the analyzer properly accounts for interferences (Zhao et al, 2012). When performing calibrations or checks, recommended practices are to select appropriate span level, preferably use gas mixtures with varying water vapor content, and observe and record concentrations of other gases to evaluate potential interferences.…”

“…However, the spectra of several gases may overlap and result in measurement errors if the interference is not considered (Zhao et al, 2012). In a laboratory setting, Zhao et al (2012) showed that the internal crosscompensation algorithm of a photoacoustic multi-gas analyzer (PAMGA) that uses PIR eliminated interferences between target gases, but was insufficient to eliminate interferences of non-target gases on target gases and had potential to cause secondary interferences. In the tests by Zhao et al (2012), the interference of water vapor was negligible for N 2 O, but CH 4 was not included in the PAMGA filter configuration for the water vapor test.…”

“…In a laboratory setting, Zhao et al (2012) showed that the internal crosscompensation algorithm of a photoacoustic multi-gas analyzer (PAMGA) that uses PIR eliminated interferences between target gases, but was insufficient to eliminate interferences of non-target gases on target gases and had potential to cause secondary interferences. In the tests by Zhao et al (2012), the interference of water vapor was negligible for N 2 O, but CH 4 was not included in the PAMGA filter configuration for the water vapor test. In broiler and dairy housing settings, Hassouna et al (2013) demonstrated an overestimation of nitrous oxide and an underestimation of CH 4 resulting from non-compensated interferences with a PAMGA.…”

NDIR Gas Sensor for Spatial Monitoring of Carbon Dioxide Concentrations in Naturally Ventilated Livestock Buildings

“…Currently applied systems to monitor CO 2 concentrations from agricultural facilities include Photo Acoustic Spectroscope (PAS) Gas Analyzer [4,6,18,19,20,21,22,23,24,25]; and the Open-Path laser (OP-laser) [26,27,28,29,30]. The OP-laser and PAS analyzer have been extensively used by researchers seeking to monitor emissions from livestock barns in the last years, mostly mechanically ventilated.…”

Methane and carbon dioxide emissions from manure storage facilities at two free-stall dairies

“…5A). While Zhao et al (2012) indicated that the PAS filter used in CO 2 concentration measurements had a water vapor interference, the difference between the NDIR and PAS measurements of CO 2 were were well correlated ( NDIR = 0.89 × PAS + 0.289, R 2 = 0.99), indicating that whatever interferences were present in the PAS measurement of CO 2 , the effect was similar across the entire measurement domain and emissions measurements based on the differences in concentration were minimally impacted (Fig. 5B).…”