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NO2 Diffusion Tube QA/QC
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As part of their provision of support to Local Authorities for air quality
management, Defra and the Devolved Administrations are providing a set of centralised
QA/QC services, to assist Local Authorities using diffusive samplers for monitoring of
ambient nitrogen dioxide (NO2) concentration, as part of their Local Air
Quality Management process.
1 Guidance on Calculation and Use of Bias Adjustment Factors
Many Local Authorities are now carrying out diffusion tube co-location studies, in which diffusion tubes are compared with automatic analysers. But when defining nitrogen dioxide diffusion tube bias, is it better to use the local co-location result or the average of as many co-location studies for the laboratory and tube preparation method as possible? For guidance on this question, please click here
Bias adjustment factors determined from co-location studies throughout the UK have been collated by the Review & Assessment Helpdesk. They are available as a spreadsheet and can be found here
For cases where use of a locally-derived bias adjustment factor is most appropriate, a spreadsheet has been developed by AEA, to assist diffusion tube users in calculating the precision and accuracy of their results, in co-location studies where diffusion tubes are compared with automatic analysers. It can be used to calculate a bias adjustment factor (with a 95% confidence interval as an estimate of the uncertainty on the bias adjustment factor), and then to apply the bias adjustment factor to annual mean results from other NO2 diffusion tube sites. Click here to download a copy of this spreadsheet. (You can also find it on the "LAQM tools" section of the Air Quality Archive at www.airquality.co.uk/archive/laqm/tools.php
2 A Web-Based Data Entry System, which provides Local Authorities with a reliable and convenient means of storing their NO2 diffusion tube data, free of charge, and of making it available to others via the Defra Air Quality Archive. Originally developed for the former NO2 Network, the system can now accept data from all Local Authority diffusion tube sites (not just those formerly in the NO2 Network). The system can accept data from multi-tube sites (e.g. triplicates), and automatic monitoring data from co-location sites can also be entered. This service is available to all UK Local Authorities. |
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- Existing users can update their NO2 data on line here
- For more information on using this system, please contact the LA Air Quality Support Helpdesk on 0870 190 6050.
3 Guidance Notes for Local Authorities using NO2 diffusion tubes for LAQM: this document is intended as a supplement to the Defra Technical Guidance LAQM.TG(03), bringing together in one convenient source the latest information and guidance on using diffusion tubes and interpreting the results. Click here to download a copy of the NO2 Diffusion Tube Guidance Notes.
4 Co-ordination of a quality assurance/quality control (QA/QC) framework, aimed at the analytical laboratories that supply and analyse the diffusion tubes. This currently comprises- Promotion of the independent Workplace Analysis Scheme for Proficiency (WASP), operated by the Health and Safety Laboratory, with yearly assessment against agreed performance criteria.
- Operation of a field intercomparison exercise, in which diffusion tubes are co-located with an automatic analyser: from January 2006 this is at a roadside site.
- Operation of a QC solution testing scheme.
Participation is recommended for any laboratory that prepares or analyses NO2 diffusion tubes used by Local Authorities for LAQM purposes.
Quarterly summaries of participating laboratories' performance in the WASP scheme over the preceding 12 months, prepared by AEA, are available by clicking on the links below:
WASP Rounds 97 - 100 (Apr 2007 - Apr 2008)
WASP Rounds 98 - 102 (Jul 2007 - Jul 2008)
WASP Rounds 99 - 103 (Oct 2007 - Oct 2008)
WASP Rounds 100 - 104 (Jan 2008 - Jan 2009)
WASP Rounds 101 - 105 (Apr 2008 - Apr 2009)
WASP Rounds 102 - 106 (Jul 2008 - Jul 2009)
WASP Rounds 103 - 107 (Oct 2008 - Oct 2009)
5 A Working Group on harmonisation of preparation and analysis methods. As part of this contract, Defra and the Devolved Administrations commissioned a Working Group, comprising representation from Defra and the Devolved Administrations, laboratories, HSL, the Environment Agency, SEPA and other stakeholders, aimed at harmonising the methodology used in preparing, utilising and analysing diffusion tubes. The Working Group's report, published in February 2008, is available here
For more information on any of the above, please contact the LA Air Quality Support Helpdesk on 0870 190 6050. |
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