Denuder

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A denuder is a measuring device that is used to measure gas components in dusty air. The measuring principle is based on the fact that components of the gas and particle phases have different diffusion speeds.

Function and use

Various denuders for atmospheric investigations by NOAA .

The sample air to be examined is sucked in laminar through a glass tube or an annular gap that is coated with a sorbent substance. In addition to the flow movement, the individual components of the sample air also exhibit a diffusion movement and also diffuse transversely to the flow direction. Since the diffusion speed of particles is orders of magnitude lower than that of gases, the latter predominantly hit the pipe wall and are deposited there. Downstream of the glass tube or annular gap is a filter for separating the particle phase. After sampling is complete, both the sorbed and the filtered phase can be analyzed.

Denuder is available in various designs, such as an annular gap or wet denuder. They can also be carried out in several stages.

The measurements with Denuders are integrating over time. Usual measurement times are between one hour and thirty days. Denuders work with sufficient accuracy that they can be used to make statements about guide values ​​and limit values.

Denuders are used in particular to detect ammonia in the outside air. They can also be used for workplace measurements for specific chemical agents. In addition to the metrological applications, denuders can be used as pre-separators to exclude cross-sensitivities : for example, as a so-called honeycomb denuder for separating ozone .

literature

  • VDI 3869 Part 3: 2010-10 Measurement of ammonia in the outside air; Sampling with coated diffusion separators (denuders); Photometric or ion chromatographic analysis (Measurement of ammonia in ambient air; Sampling with diffusion separators (denuders); Photometric or ion chromatographic analysis). Beuth Verlag, Berlin. ( Summary and table of contents online ).

Individual evidence

  1. ^ A b Franz Joseph Dreyhaupt (Ed.): VDI-Lexikon Umwelttechnik. VDI-Verlag Düsseldorf 1994, ISBN 3-18-400891-6 , pp. 324-325.
  2. ↑ Ulrich Dämmgen, Lotti Thöni, Ralf Lumpp, Kerstin Gilke, Eva Seitler, Marion Bullinger: Process parameters for the determination of ammonia concentrations in the ambient air - Part 1: Measurements with Denuders. In: Hazardous substances - cleanliness. Air . 70, No. 5, 2010, ISSN  0949-8036 , pp. 197-201.
  3. ↑ DIN EN 13936: 2014-04 Exposure at the workplace; Measurement of a chemical agent present as a mixture of airborne particles and steam; Requirements and test methods; German version EN 13936: 2014. Beuth Verlag, Berlin, p. 11.
  4. ↑ Harald Creutznacher, Klaus Huber: Ozone cross-sensitivity in the immission measurement of particulate matter-accumulated benzo [a] pyrene. In: Hazardous substances - cleanliness. Air. 62, No. 7/8, 2002, ISSN  0949-8036 , pp. 319-324.