| Popis: |
Publisher Summary This chapter discusses the quantitative aspects of dynamic generation of test atmospheres. Dynamic methods are used to generate known ambient pollutant concentrations. They involve the continuous mixing of two or more measured flows of constituent gases. They have advantages over static gravimetric methods in that long-term stability of the mixture is unimportant and adsorption losses of minor constituents are not troublesome once equilibrium has been reached with the surface of the apparatus, their major disadvantage being their complexity. Generation of primary standards for air pollution measurement has to be performed carefully under optimal conditions by highly qualified personnel and requires continuous checks on generation processes. Hence, the generation of primary standards is costly and is tied to a laboratory. For most pollutants, the continuous production of known amounts is based on permeation tubes. The basic quantitative aspects producing standards with permeation tubes are (1) measurement of the dilution flow rate, permeation rate, and moisture supply; (2) stability of dilution flow, permeation rate, and moisture supply; (3) residual measurand content of cleaned dilution air; and (4) loss of measurand during transport in the generator. |
