Long-term reliability of the Figaro TGS 2600 solid-state methane sensor under low Arctic conditions at Toolik lake, Alaska

• Main Authors: Eugster, Werner, Laundre, James, Eugster, Jon, Kling, George W.
• Format: Text
• Language: English
• Published: 2019
• Subjects: Arctic; Alaska
• Online Access: https://doi.org/10.5194/amt-2019-402; https://www.atmos-meas-tech-discuss.net/amt-2019-402/

The TGS 2600 was the first low-cost solid state sensor that shows a weak response to ambient levels of CH 4 (e.g., range ≈1.8–2.7 ppm). Here we present an empirical function to correct the TGS 2600 signal for temperature and (absolute) humidity effects and address the long-term reliability of two identical sensors deployed from 2012 to 2018. We assess the performance of the sensors at 30-minute resolution and aggregated to weekly medians. Over the entire period the agreement between TGS-derived and reference CH 4 concentrations measured by a high-precision Los Gatos Research instrument was R 2 = 0.42, with better results during summer (R 2 = 0.65 in summer 2012). Using absolute instead of relative humidity for the correction of the TGS 2600 sensor signals reduced the typical deviation from the reference to less than ±0.1 ppm over the full range of temperatures from −41 °C to 27 °C. At weekly resolution the two sensors showed a downward drift of signal voltages indicating that after 10–13 years a TGS 2600 may have reached its end of life. While the true trend in CH 4 concentrations measured by the high-quality reference instrument was 10.1 ppb yr −1 (2012–2018), part of the downward trend in sensor signal (ca. 40–60 %) may be due to the increase in CH 4 concentration, because the sensor voltage decreases with increasing CH 4 concentration. Weekly median diel cycles tend to agree surprisingly well between the TGS 2600 and reference measurements during the snow-free season, but in winter the agreement is lower. We suggest developing separate functions for deducing CH 4 concentrations from TGS 2600 measurements under cold and warm conditions. We conclude that the TGS 2600 sensor can provide data of research-grade quality if it is adequately calibrated and placed in a suitable environment where cross-sensitivities to gases other than CH 4 is of no concern.