RESUMEN
A high-precision analytical system to observe the variations in the amount fractions of atmospheric oxygen with a very small uncertainty was developed. The system comprises a magneto-pneumatic oxygen analyzer and three automatic pressure controllers. The drift of the analyzer's signal intensity can be reduced when the amount fractions of oxygen in the sample and reference gases are similar because the temperature coefficient of the analyzer linearly depends on the difference between these amount fractions. The repeatability of oxygen determination and the long-term stability of the system were tested to assess the applicability of the analyzer to field-based measurements for continuous atmospheric observations. The standard deviation of the average for 10-min measurements in the 5-day long-term stability test was 0.7 µmol mol-1 after a temperature correction. This indicates that the system can continuously measure the amount fractions of oxygen in the atmosphere for a few days without interruption for any calibration and/or compensation for the signal drift.