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National Bias Adjustment Factors


A database of bias adjustment factors determined from local authority co-location studies throughout the UK has been collated by the Local Air Quality Management Helpdesk. Using orthogonal regression, combined bias adjustment factors have been calculated for each laboratory, year and preparation method combination for which data are available.

The database, which is in the form of an Excel spreadsheet, is updated regularly and can be downloaded below.

The current version (09/22) of the diffusion tube bias adjustment factors spreadsheet was released in September 2022. This provides the final round of National Diffusion Tube Bias Adjustment Factors for 2021 diffusion tube monitoring data.

The next update, which will be the first iteration to incorporate diffusion tube co-location studies for 2022, is due March 2023 (Round 1 of 3). It is recommended that all local authorities who have carried out a co-location study should add the results to the database of combined bias adjustment factors. To do this, you should fill in the questionnaire provided on the Adding your Co-location Data page.

Current Version


Diffusion Tube Bias Adjustment Factors Spreadsheet

Released: September 2022 (XLSX, 840 KB)

Diffusion Tube Co-location Methodology

Released: March 2006 (PDF, 167 KB, 3 pages)

LAQM Helpdesk
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