Ammonia Diffusive Sampler
The diffusive sampler for ammonia collects gaseous ammonia by absorption on phosphoric acid. The amount of ammonia is determined spectrophotometrically by the indophenol method. The passive samplers are composed of a polypropylene housing with an opening of 20 mm diameter. To reduce wind disturbance a teflon membrane is attached, supported by a wire net. To protect the sampler from weather influences, as well as minimising wind disturbance, a protective shelter has to be used.
Time series of a comparison of a continuous NH3 analyser and diffusion tube of ammonia .
Samplingrate: 31.5 ml/min at 20oC
Working range: 0.5 — 20 µg/m3
Sampling time: 2— 4 weeks
Detection limit: 0.3 µg/m3 for one month
wind speed: Influence of wind speed < 10% up to 4.5 m/sec using protection shelters
temperature: no influence between 5 to 40oC
humidity: no influence between 20 to 80%
before use: 6 months above citric acid
after exposure: 4 months
Cross sensitivity: Solid particulates of ammonia are not collected
Expanded uncertainty*: 24.8 % at concentration levels of 5 µg/m3