The Relaxed Eddy Accumulation System (REA) developed by Agriculture and Agri-Food Canada and integrated by the National Research Council of Canada on its Twin Otter atmospheric research aircraft was first described at the Seventh SMOI in 1991. Since then the system has undergone a number of refinements and changes in the gas collection medium (steel canisters, foam plugs, and PTFE and Teflon bags) for the collection of specific trace gas species (CO₂ and VOC's, pesticides, methane and N₂O). In recent years, the focus has been on measuring the vertical flux of N₂O, which is an important contributor to the enhanced greenhouse effect. In Canada, it is estimated that 2/3 of the greenhouse gas emissions produced by the agricultural sector are due to N₂O. In order to improve these estimates and verify emission models, the REA system is being used in the Twin Otter to make regional measurements of N₂O emissions, while tower and chamber systems make simultaneous site-specific estimates.

The release of N₂O is sporadic, often occurring in bursts. Tower-based measurements have demonstrated that 50-75 percent of the annual emissions of N₂O in Eastern Canada occur in early spring during and after snowmelt. In the springs of 2000 and 2001, the Twin Otter was used to make repeated passes on two agricultural tracks in Eastern Ontario over periods of a few weeks. Emission rates of up to 120 ng/m²/s were measured in a sharply defined 'spring burst' lasting just a few days. In the spring of 2002, a similar study was conducted in Saskatchewan in a 10x10 km area that was simultaneously sampled by an array of chambers. The aircraft-measured emission rates were found to be small, at only 4-5 times the detection limit of the system (approximately 5 ng/m²/s), due to the unusually dry spring. The aircraft data will be presented along with tower and chamber measurements of the N₂O fluxes.