A floating rectangular polyvinyl chloride (PVC) open bottom chamber coupled with a molecular sieve trap was designed to measure the amounts of nitrous oxide gas (N2O) emitted during aerobic treatment or storage of liquid animal slurries. A number of outdoor calibration trials, using water and a standard gas mixture, resulted in an averageN2O recovery of 79$8%. Further experiments carried out on a farm scale aerobic treatment unit confirmed the reliability and ease of use of the method.