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. Local authorities should use the most up-to-date data and supporting tools made available.

The current 2015 reference year background maps and the earlier versions can be found here.

Users of the 2015 reference year background maps in Central London should be aware that the impact of the Ultra Low Emission Zone (ULEZ) from 2020 onwards IS now included by default - users no longer need to adjust the data to account for the ULEZ.

The main aspects of the background maps and comprehensive guidance on the use of the related tools can be found in the current Background Maps User Guide (PDF, 869KB, 42 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 (v6.1) should only be used with the 2015 reference year background maps and the Emissions Factors Toolkit v8.0 onwards, and can be used for years 2015 to 2030.

The current version of the calculator (version 6.1, 17 October 2017) can be downloaded here (XLS, 6.8MB). The basis for the f-NO2 values and background maps used in version 6.1 of the calculator are available here (PDF, 71KB, 1 page).

The previous version of the calculator for use with the 2013 reference year background maps 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 2015 reference year background maps and the EFT v8.0 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 current Background Maps User Guide (PDF, 869KB, 42 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 current version of the tool (v6.0) should only be used with the 2015 reference year background maps, and can be used for years 2015 to 2030.

The current version of the tool (version 6.0, November 2017) can be downloaded here (ZIP, 2.3MB).

The previous version of the tool for use with the 2013 reference year background maps 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 2015 reference year background maps and the EFT v8.0 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 current Background Maps User Guide (PDF, 869KB, 42 pages). 

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Year Adjustment Factors

Year adjustment factors are not required for 2015 reference year background maps because maps are available for all years 2015-2030.

The Year Adjustment Factors published in the 2003 Technical Guidance LAQM TG(03) may still be used for projecting 2001 reference year background concentrations of carbon monoxide, benzene and 1,3-butadiene ONLY. These are available here (XLS, 33KB). Before using these, please read the current Background Maps User Guide (PDF, 869KB, 42 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.