Passive Flux Samplers to measure Nitrous Oxide and Methane Emissions from Agricultural Sources, Part 2: Desorption Improvements

In the first part of this research work, it was shown that it was feasible to adsorb nitrous oxide (N 2 O) and methane (CH 4 ) on to molecular sieves loaded into standard stainless-steel gas sampling tubes. Of three types of sieve examined, zeolite 5A molecular sieve gave the best performance. A thermal desorption procedure was used to recover the gas adsorbed. However, the average efficiency for desorption of N 2 O and CH 4 was respectively 59% and 6% for zeolite 5A molecular sieve. The objective of the present study was to develop a complete desorption procedure for N 2 O and CH 4 absorbed on zeolite 5A molecular sieve. The parameters investigated were: desorption gas flow rate, desorption duration and temperature. The complete procedure includes a two-stage desorption using in first stage a flow rate of 21 m l  min −1 and 40 min purge period. A flow rate of 64 m l  min −1 and 15 min purge period was used for the second stage. In this study, five temperatures were investigated (50, 100, 150, 200 and 250 °C). The N 2 O desorption efficiency was not significantly influenced by the temperature. A temperature of 100 °C was recommended for a desorption efficiency of N 2 O ranged from 75% to 94%, with an average of 88%. For CH 4 , the second stage desorbs almost the same amount as does the first stage and the desorption temperature has significant effect. Together, the two stages allowed recovery of up to 51% of the total amount of CH 4 absorbed.