Use of silicone tubing to sample nitrous oxide in the soil atmosphere

Although a number of techniques have been developed for sampling gaseous compounds in the soil atmosphere, their performance in saturated soil environments is usually less than satisfactory. We have evaluated the use of silicone tubing materials to sample nitrous oxide (N2O), an important component of anoxic soil atmospheres. Sections of regular (wall thickness, 2.4 mm) and reinforced (wall thickness, 4.8 mm) silicone tubing were placed into Mason jars and exposed to three concentrations of N2O (30, 45 and 60 μl l−1) at three different temperatures (4, 22 and 30°C). The transfer of N2O from the jar headspace into the silicone tubing was monitored over 2 to 3 h. The transfer of N2O was described by both a polynomial equation and by a first order diffusion model. The regular silicone tubing is more permeable than the reinforced silicone tubing due probably to thickness difference as well as to differences in manufacturing and composition. At 22°C, it was estimated, using a first order model, that N2O concentrations inside the regular silicone tubing and the jar headspace would come to equilibrium within 4.4 h contrasting with the 8.2 h needed with the reinforced silicone tubing. The performance of the soil atmosphere samplers made of regular silicone tubing was tested in alternatively saturated and unsaturated soil columns. Results obtained confirmed the suitability of silicone tubing for soil N2O sampling and other similar applications.