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Adding your Co-location Data


Bias adjustment factors determined from local authority co-location studies throughout the UK have been collated by the Local Air Quality Management Helpdesk. They are available as a spreadsheet database from the National Bias Adjustment Factors page.

To help keep this database up to date, it is recommended that all local authorities who have carried out a co-location study in which NO2 diffusion tubes have been exposed alongside an automatic (chemiluminescent) NO2 analyser, for nine or more months in any calendar year, send their data for inclusion. In order to keep this inventory up to date, we ask that all Local Authorities to supply us with their most recent data, even if this is not yet ratified (there is the opportunity to update provisional data later in the year).

The Local Air Quality Management Technical Guidance LAQM.TG(22) recommends that where possible, Local Authorities should verify their nitrogen dioxide diffusion tubes by co-locating them with an automatic monitor. it is recommended that in many situations, Local Authorities should use the combined results of a number of co-location studies, so as to minimise the uncertainty associated with any single study. Because of this, an important part of interpreting nitrogen dioxide diffusion tube data in the UK is to consult the inventory of bias adjustment factors, maintained and operated by the National Physical Laboratory (NPL) on behalf of Defra and the Devolved Administrations.

We appreciate submission of co-location study data to populate the National Bias Adjustment Spreadsheet. To add your co-location data to the database, please click on the link below to download a questionnaire, which provides all the information and contact details you need.

Current Version


Diffusion Tube Co-location Data Questionnaire

Released: January 2024 (.XLSX, 65 KB)

Please Note: The next version of the National Bias Adjustment Spreadsheet is due in June 2024, which will incorporate diffusion tube monitoring data for 2023. To ensure your study is included (pending data quality checks) please return your questionnaire by the start of the month.

LAQM Helpdesk
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