Investigation of adsorption and desorption behavior of small-volume cylinders and its relevance for atmospheric trace gas analysis

Abstract

Atmospheric trace gas measurements of greenhouse gases are critical in their precision and accuracy. In the past 5 years, atmospheric measurement and gas metrology communities have turned their attention to possible surface effects due to pressure and temperature variations during a standard cylinder's lifetime. This study concentrates on this issue by introducing newly built small-volume aluminum and steel cylinders which enable the investigation of trace gases and their affinity for adsorption and desorption on various surfaces over a set of temperature and pressure ranges. The presented experiments are designed to test the filling pressure dependencies up to 30 bar and temperature dependencies from-10 °C up to 180 °C for these prototype cylinders. We present measurements of CO2, CH4, CO and H2O using a cavity ring-down spectroscopy analyzer under these conditions. Moreover, we investigated CO2 amount fractions using a novel quantum cascade laser spectrometer system enabling measurements at pressures as a low as 5 mbar. This extensive dataset revealed that for absolute pressures down to 150 mbar the enhancement in the amount fraction of CO2 relative to its initial value (at 1200 mbar absolute) is limited to 0.12 μmol mol-1 for the prototype aluminum cylinder. Up to 80 °C, the aluminum cylinder showed superior results and less response to varying temperature compared to the steel cylinder. For CO2, these changes were insignificant at 80 °C for the aluminum cylinder, whereas a 0.11 μmol mol-1 enhancement for the steel cylinder was observed. High-temperature experiments showed that for both cylinders irreversible temperature effects occur especially above 130 °C.