Background Maps

About the Background Maps and User Guide

Air pollution background concentration maps are published by Defra and the Devolved Administrations to assist local authorities in carrying out Review and Assessment of local air quality as part of their duties under the Environmental Act 1995.

The main purpose of the background maps is to provide estimates of background concentrations for specific pollutants. These can then be used in air quality assessments to better understand the contribution of local sources to total pollutant concentrations. They provide information on how pollutant concentrations change over time and across a wide area; they also provide an estimated breakdown of the relative sources of pollution. The maps allow for the assessment of new pollutant sources that are introduced into an area and the impact they may have upon local air quality.

Background maps are updated by Defra periodically due to updates to underlying data including emissions factors. In recent years there have been annual updates due to new information on NOx emissions from diesel vehicles. Fleet and vehicle activity data have also been updated. Local authorities should use the most up-to-date data available.

The current 2013 reference year background maps version and the earlier versions can be found here.

Users of the 2013 reference year background maps in Central London should be aware that the impact of the Ultra Low Emission Zone (ULEZ) IS NOT included by default. A new procedure for adjusting the provided NOx and NO2 background maps to be (approximately) inclusive of the impact of the ULEZ on the road transport contribution to background NOx concentrations is now provided.

The main aspects of the background maps and comprehensive guidance on the use of the related tools, including how to apply the ULEZ adjustment procedure, can be found in the Background Maps User Guide.

The current Background Maps User Guide can be found here (PDF, 925KB, 39 pages).

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NOx to NO2 Calculator

This calculator allows users to derive NO2 from NOx wherever NOx is predicted by modelling emissions from roads. The calculator can also be used to calculate the road component of NOx from roadside NO2 diffusion tube measurements.

The current version of the calculator (v5.1) should only be used with the 2013-based background maps and the Emissions Factors Toolkit v7.0 onwards, and can be used for years 2013 to 2030.

The current version of the calculator (version 5.1, 3 June 2016) can be downloaded here (XLS, 6.8MB). The basis for the f-NO2 values and background maps used in version 5.1 of the calculator are available here (PDF, 10KB, 1 page).

The previous version of the calculator is available below:

Local authorities are advised to use the latest version of the calculator for all future work that is based upon use of the 2013-based background maps and the EFT v7.0 onwards. However, if earlier versions of the calculator are required, please contact the Helpdesk for further assistance.

Guidance on how to use the NOx to NO2 Calculator is available in the Background Maps User Guide here (PDF, 925KB, 39 pages).

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NO2 Adjustment for NOx Sector Removal Tool

If users subtract emission sectors from the NOx map, they must update the NO2 map accordingly. This tool allows users to perform this adjustment. The tool can also be used to adjust the background maps for areas within the London Ultra Low Emission Zone (ULEZ) to be (approximately) inclusive of the impact of the ULEZ from 2020 onwards.

The current version of the tool (v5.1) should only be used with the 2013-based background maps, and can be used for years 2013 to 2030.

The current version of the tool (version 5.1, October 2016) can be downloaded here (XLS, 9.5MB).

The previous version of the tool is available below:

Local authorities are advised to use the latest version of the tool for all future work that is based upon use of the 2013-based background maps and the EFT v7.0 onwards. However, if earlier versions of the tool are required, please contact the Helpdesk for further assistance.

Guidance on how to use the NO2 Adjustment for NOx Sector Removal Tool is available in the Background Maps User Guide here (PDF, 925KB, 39 pages). 

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Year Adjustment Factors

Year adjustment factors are not required for 2013-based background maps because maps are available for all years 2013-2030.

The Year Adjustment Factors published in the 2003 Technical Guidance LAQM TG(03) may still be used for projecting 2001-based background concentrations of carbon monoxide, benzene and 1,3-butadiene ONLY. These are available here (XLS, 33KB). Before using these, please read the Background Maps User Guide here (PDF, 925KB, 39 pages).

For SO2, year adjustment factors are no longer provided because it is considered that away from specific locations near industrial sources or areas of high domestic coal burning, SO2 background levels would change very little, i.e. the factor would be close to one. Continuous monitoring data of SO2 is also available from the UK-AIR website.

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Important: Please save these files to a local drive before using by right-clicking the link and choosing Save Target As... or Save Link As..., as they may not function correctly if opened directly from the link in your browser window.