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A gas diluter based on critical orifices was built and evaluated. The gas diluter is capable of creating dilution ratios of 1:1400 at a total flow of 6.5 L/min. An extended uncertainty analysis of gas concentrations and dilution ratios according to the Guide to the Expression of Uncertainty in Measurement was conducted. A gas cylinder of 5.16 ppm <i>NO</i>₂ with a relative uncertainty of 1.5% (k = 1) can be diluted down to a concentration of 3.69 ppb <i>NO</i>₂ (dilution ratio of 1:1400) at an uncertainty of 1.9% (k = 1). The results are in good agreement with reference <i>NO</i>₂ measurements, conducted with a chemiluminescence detector (CLD, European reference method EN14211; 2005).