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Environmental monitoring

Ozone photometer and NOX analyser services

We provide UKAS accredited ozone photometer & NOX analyser calibration services

Standard Reference Photometer 

The NIST Standard Reference Photometer serial number 20 owned by NPL is the primary ozone standard of the UK. This is a UV photometric device that precisely monitors ozone concentrations in air up to 1000 nmol mol-1.

NPL is accredited by UKAS to ISO 17025 to perform the calibration of ozone photometers up to 50 µmol mol-1.

NOX analyser calibration 

NPL is accredited by UKAS to perform the calibration of NOX analysers between 100 nmol mol-1 to 10 µmol mol-1 with an expanded measurement uncertainty (k = 2) of 3.5%. 

The reference materials (RMs) used for this calibration service are certified against NPL nationally-traceable gravimetrically-prepared cylinders of NO in nitrogen at nominal concentrations of 10 µmol mol-1 to 100 µmol mol-1.  These RMs are diluted to a concentration close to that of the artefact being certified. The measurement principle of the analytical technique used is that of chemiluminescence using ozone. 

NPL can also perform measurements of conversion efficiency of NO2 to NO and linearity checks in each range requested by the customer. 

Calibration of NOx analysers are typically carried out at the customer’s monitoring site. 

Ongoing intercomparison BIPM.QM-K1 for Ozone at ambient level 

To evaluate the degree of equivalence of ozone photometers that are maintained as national standards within international networks for ambient ozone measurements, NPL has been running the intercomparison BIPM.QM-K1 since 2004 with a new round every four years (see example report). The most recent comparison was in June 2022 and its results will be available shortly.

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