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

Abstract

Abstract. The TGS 2600 was the first low-cost solid state sensor that shows a weak response to ambient levels of CH4 (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 CH4 concentrations measured by a high-precision Los Gatos Research instrument was R2 = 0.42, with better results during summer (R2 = 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 CH4 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 CH4 concentration, because the sensor voltage decreases with increasing CH4 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 CH4 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 CH4 is of no concern.