NPL has world-leading expertise in the procedures used to assure the quality of all types of environmental gas measurements. Gas analysers require regular calibration and quality control in order to provide reliable results. NPL's expertise covers:

• Site audits
• Operations audits
• Staff training

NPL's QA/QC audits are regularly carried out on the semi-automatic monitoring stations that provide important information on the UK's urban and rural air quality. Such audits can provide the external verification required for measurement procedures to stand up to public or legal scrutiny.

A thorough QA/QC audit by NPL will report on:

• Optimum site location
• Data handling
• Suitability of instrumentation
• Statistical procedures
• Best operating practices
• Documentation
• Procedures and frequency for calibration
• Compatibility with national network standards

Site Audits

Site audits form a comprehensive set of instrument performance tests, identical to those currently performed for Defra Networks, and fully compliant with the requirements of EU monitoring set out in the relevant CEN standards. The separate elements of audits are:

• To carry out performance tests on the air quality instruments to determine whether they are operating satisfactorily:
  • Parameters tested on gas monitoring instruments are typically: accuracy, linearity, noise levels (at zero and span), rise and fall times, and NOx analyser converter efficiency using gas phase titration. Sample lines and analysers would be tested for leaks
  • For PM TEOM instruments, the sampling and bypass flow rates are measured with UKAS calibrated flow meters, and the Ko factor determined with UKAS certified masses
  • For optical and beta-attenuation PM instruments, the sampling and bypass flow rates are measured with UKAS calibrated flow meters. Sample lines and analysers would be tested for leaks
• To determine the on-site calibration cylinder concentrations by reference to nationally-traceable (UKAS certified) standards, and to compare them with the given values
• To check sites for local factors which might be affecting the validity of the data
• To provide on site assistance and training to Local Site Operators

Losses of pollutants in the sampling lines can also be measured.

UKAS certificates covering all accredited measurements are issued. NPL has been accredited by UKAS under ISO 17025 as competent to perform all the field measurements – not just the calibrations - required for UK National Air Quality Networks.

Data Ratification

Data ratification is the process whereby raw or provisional data are combined with all other relevant information to derive the best final dataset, which is as accurate as possible and has known measurement uncertainties to allow meaningful comparison with other data.

NPL offers a data ratification service using sophisticated data handling software and benefiting from our long association with National Networks and European regulation.

Contact

Customer Service tel: +44 20 8943 8637
E-mail: environmental_enquiries@npl.co.uk