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