VDI 2453 BLATT 2
Gaseous air pollution measurement - Measurement of concentration of nitrogen monoxide and nitrogen dioxide - Calibration of NO/NOx chemiluminescence analysers using gas phase titration
| Organization: | VDI |
| Publication Date: | 1 October 2002 |
| Status: | active |
| Page Count: | 20 |
| ICS Code (Ambient atmospheres): | 13.040.20 |
scope:
Introduction
Guideline series VDI 2453 comprises a number of parts which give instructions for measuring nitrogen monoxide (NO) and nitrogen dioxide (NO2) in ambient air, and for calibrating automatic analysers.
The individual parts of this guideline series specify a manual analytical method [1] and methods for preparing calibration gases to calibrate automatic instruments [2]. This Part 2 specifies a calibration method using gas phase titration (GPT). It can be applied to all automatic analysers based on the chemiluminescence measuring principle.
Instruments for determining nitrogen oxide concentrations in ambient air are generally calibrated using nitrogen monoxide calibration gases [2]. Analysers using the chemiluminescence principle, equipped with a converter, play a dominant role, since they measure simultaneously nitrogen monoxide and the total of the nitrogen monoxide and nitrogen dioxide (NOx = NO + NO2). Nitrogen dioxide is calculated as the difference between the concentrations measured in the two analytical channels of the analyser. Using the gas phase titration of NO with ozone (O3) and tracing the results back to the reference measurement method
the NO and NOx channels can be calibrated
the converter efficiency can be determined
if necessary, the NO concentration in the calibration gas used can be determined
For the use of the method described in this guideline it is not necessary to know the exact NO concentration in the NO calibration gas used. However, the NO concentration can be determined as part of the calibration procedure. The concentration of O3 produced for gas phase titration, which is equivalent to the concentration of NO2 formed, can as an alternative also be determined by UV photometry as the reference measurement method [3; 4]. Additional calibration of ozone analysers using the gas phase titration procedure is described in the annex.
In addition to commercially available calibration gas generators, home-made types that enable controlled ozone generation can also be used for gas phase titration.
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