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Annualisation of Diffusion Tubes


The process of annualisation allows for annual mean pollutant concentrations to be estimated from extrapolation of short-term monitoring results.

This annualisation tool has been developed to assist local authorities to annualise NO2 diffusion tube monitoring data at sites with less than 9 months’ usable data. The methodology consists of using NO2 concentration data from nearby continuous background monitoring sites to assist in estimating the annual mean NO2 concentrations from a diffusion tube site(s). See para 7.140 of Technical Guidance LAQM.TG(22) for more information.

Current Version


Annualisation Tool v1.0

Released: June 2020 (XLSB, 1.0 MB)


The following inputs are required:

Diffusion Tube Calendar Inputs – Select the annualisation year to auto populate with the default calendar dates. Check the start and end dates are correct and make any manual adjustments to the default calendar dates in line with the specific monitoring programme undertaken.

Diffusion Tube Inputs – Input the calculated bias adjustment factor that will be applied to all diffusion tube sites entered into the tool and enter the diffusion tube monthly raw data for each diffusion tube site.

Continuous Monitor Inputs – Check the pre-populated Start Date and Start Time for the continuous monitor datasets are correct and make any manual adjustment as necessary. Enter hourly NO2 concentration data from two to four nearby background continuous monitoring sites. Ensure the period for which continuous monitoring data are entered spans the entirety of the Annualisation Year Start and End Dates as defined on the Diffusion Tube Calendar Inputs tab. Ideally the continuous monitoring sites should meet the selection criteria as specified in Box 7-9 of LAQM.TG(22) and form part of the national network.


Please Note: The diffusion tube data processing tool is also available and is recommended to be used for processing all diffusion tube data in line with the annual reporting requirements.

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