Measuring CO2 and CH4 with a portable gas analyzer: Closed-loop operation, optimization and assessment

• DOI: 10.1371/journal.pone.0193973
• Publication Date: 2018-04-04T13:30:28Z
• Authors: Jeremy Wilkinson; Christoph Bors; Florian Burgis; Andreas Lorke; Pascal Bodmer
• Keywords: Air Pollutants; Science; Climate Change; Q; R; Equipment Design; Carbon Dioxide; 01 natural sciences; 6. Clean water; Atmospheric Pressure; Calibration; Medicine; Methane; Research Article; Environmental Monitoring; 0105 earth and related environmental sciences

The use of cavity ring-down spectrometer (CRDS) based portable greenhouse gas analyzers (PGAs) in closed-loop configuration to measure small sample volumes (< 1 l) for CH4 and CO2 concentrations is increasing offers certain advantages over conventional measurement methods terms speed as well the ability directly field locations. This first systematic assessment uncertainties, problems issues associated with achieving reliable repeatable this technique presents adaptation, range, calibration maintenance, accuracy efficient operation, one example instrument. Regular open-loop calibration, a precise loop volume estimate, leak free system, high standard injection practices are necessary accurate results. For 100 μl injections, measured values ranging from 4.5 9 x104 ppm (CH4), 1000 x106 (CO2) possible uncertainties ±5.9% ±3.0%, respectively, beyond correction may be necessary. Uncertainty arising variations water vapour content atmospheric pressure (0.24% -0.9% +0.5%, respectively). With good practice, individual operator repeatability 1.9% (CH4) 2.48% can achieved. Between error was around 3% both gases four operators. Slow syringe plunger operation (> 1s) recommended; generally delivered more (ca. 3-4%) into closed instrument than did rapid operation. Automated value retrieval we achieved 3 5-fold time reduction each cycle <2 min), reading, recording, digitization errors eliminated.