Methods

Ammonia monitoring with the Willems-badge passive-diffusive sampler

Ammonia gas concentration is monitored using a passive-sampling method, the so-called "Willems-badge". The sampling device is a "badge" because it is a shallow cylinder, rather like a badge or button. To collect ammonia, the badge is placed, in the open air, on a supporting structure at a height of 1.2 meters above ground level.  The badge contains a sorbent surface that traps ammonia, and a fixed-depth space defined by a spacer and a filter, creating a uniform-length diffusion gradient. The lid is taken off during exposure, and replaced afterwards: with the lid in place, the badge can travel by post between the laboratory and the monitoring site.

The Willems-badge sampler works well for low ambient concentrations, and high wind speeds—both typical in Irish conditions. The method has been tested against other passive-diffusive samplers, and calibrated using active denuder samplers.