Sampling systems for isotope ratio mass spectrometry of atmospheric ammonia

Passive and active ammonia (NH3) sampling devices have been tested for their nitrogen (N) capture potential and 15N fractionation effects. Several sampling techniques produced significantly different 15NH3 signals when sampling the same NH3 source released from field site fumigation campaigns. Conventional passive NH3-monitoring systems have shown to provide insufficient N for isotope-ratio mass spectrometry and various modified devices have been developed, based on existing diffusion tube designs, to overcome this problem. The final sampler design was then tested in a wind tunnel to verify that sampling NH3 in different environmental conditions did not significantly fractionate the 15N signal.