EN 14211-2012 pdf download.Ambient air – Standard method for the measurement of the concentration of nitrogen dioxide and nitrogen monoxide by chemiluminescence.
FEP perfluoro-ethylene-propene
MFC mass flow controller
PTFE polytetrafluoroethylene
5 Principle
5.1 General
This standard describes the method for measurement of the concentrations of nitrogen dioxide and nitrogen monoxide in ambient air by means of cherniluminescence. The requirements, the specific components of the chemiluminescence analyser and its sampling system are descnbed. A number of performance characteristics with associated minimum performance criteria are given for the analyser. The actual values of these performance characteristics for a specific type of analyser shall be determined in a so-called type approval test for which procedures have been described. The type approval test comprises a laboratory test and a field test. The selection of a type-approved analyser for a specific measuring task in the field is based on the calculation of the expanded uncertainty of the measurement method. In this expanded uncertainty calculation, the actual values of various performance characteristics of a type-approved analyser and the site-specific conditions at the monitoring station are taken into account (see 9,6). The expanded uncertainty of the method shall not exceed 15% for fixed measurements or 25 % for indicative measurements, as specified in Annex I of Directive 2008/50/EC LII. Requirements and recommendations for quality assurance and quality control are given for the measurements in the field (see 9.4).
5.2 Measuring principle
Chemiluminescence is based on the reaction of nitrogen monoxide with ozone. In a chemiluminescence analyser. air is sampled through a filter (to prevent contamination of the gas conveying system, especially the optical components of the analyser) and fed at a constant flow rate into the reaction chamber of the analyser, where it is mixed with an excess of ozone for the determination of nitrogen monoxide only. The emitted radiation (chemiluminescence) is proportional to the number of nitrogen monoxide molecules in the detection volume and thus proportional to the concentration of nitrogen monoxide. The emitted radiation is filtered by a selective optical filter and converted into an electric signal by a photomultiplier tube or a photodiode.
For the determination of nitrogen dioxide, the sampled air is fed through a converter where the nitrogen dioxide is reduced to nitrogen monoxide and analysed in the same way as previously described. The electrical signal obtained from the photomuttiplier tube or photodiode is proportional to the sum of concentrations of nitrogen dioxide and nitrogen monoxide. The amount of nitrogen dioxide is calculated from the difference between this concentration and that obtained for nitrogen monoxide only (when the sampled air has not passed through the converter).
Chemiluminescence is the emission of light during a chemical reaction. During the gas-phase reaction of NO and ozone light with an intensity proportional to the concentration of NO is produced when electrons of the excited NO2 molecules decay to lower energy states.
The NO is then analysed according to the reactions (1) and (2).
The concentrations of nitrogen dioxide and nitrogen monoxide are directly measured in volumelvolume units (if the analyser is calibrated using a volume/volume standard), since the emitted radiation from the chemiluminescence reaction is proportional to the concentration of nitrogen monoxide in volume/volume units. The final results for reporting are expressed in pg/rn3 using standard conversion factors (see Clause 10).
5.3 Type approval test
The type approval test is based on the evaluation of performance characteristics determined under a prescribed series of tests. In this European Standard, test procedures are descnbed for the determination of the actual values of the performance characteristics for at least two analysers in a laboratory and the same analysers in the field, operated in parallel in both cases. The type approval laboratory tests shall not include the sampling inlet, sampling system and external data acquisition system, but shall include analyser sampling line and filter. The type approval field test may include a sampling inlet and a sampling system. However the influence of these components on the test results shall be minimised by proper maintenance.
A designated body shall perform these tests. The evaluation for type approval of an analyser is based on the calculation of the expanded uncertainty In the measuring result based on the numerical values of the tested performance characteristics and compared with a prescribed maximum uncertainty.
The type approval of an analyser and subsequent QA and QC procedures provide evidence that the defined requirements concerning data quality laid out in Annex I of Directive 2008/50/EC (ij can be satisfied.
Appropriate experimental evidence shall be provided by
— type approval tests performed under conditions of intended use of the specified method of measurement, and
— calculation of expanded uncertainty of results of measurement by reference to ENV 13005.
5.4 Field operation and quality control
Prior to the installation and operation of a type-approved analyser at a monitoring station, an expanded uncertainty calculation shall be performed with the actual values of the performance, obtained during the type approval tests, and the site-specific conditions at that monitoring station. This calculation shall be used to demonstrate that the type-approved analyser meets the requirements for all applicable limit values under the actual conditions present at that specific monitoring station.
After the installation of the approved analyser at the monitoring station, its correct functioning shall be tested.
Requirements for quality assurance and quality control are given for the operation and maintenance of the sampling system, as well as for the analyser, to ensure that the uncertainty of subsequent measurement results obtained in the field is not compromised.EN 14211-2012 pdf download.
EN 14211-2012 pdf download
PS:Thank you for your support!
