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Year Adjustment Factors


Year Adjustment Factors are detailed in the document below. These are not required for 2018 reference year background maps because maps are available for all years 2018-2030.

However, 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. Before using these, please read the current Background Maps User Guide. It should be noted that the Year Adjustment Factors should only be used for the pollutants listed above.

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.

Local authorities may need to estimate background concentrations in specific years, or project forward results from air quality monitoring surveys. A number of different approaches can be used, depending upon whether the site is background or roadside. Full details of these approaches are provided in para 7.75-7.80 of Technical Guidance LAQM.TG(22).


Year Adjustment Factors

Released: December 2021 (XLSX, 13 KB)


Please note that the Year Adjustment Factors for NOx, NO2 and PM10 are retained for historic record only – the latest version of the background maps for the required year should be used instead of applying these factors (i.e. no adjustment is necessary).

The Year Adjustment Factors for carbon monoxide, benzene and 1,3-butadiene ONLY may still be used for projecting 2001-based background concentrations of these pollutants.

For further support, please contact the LAQM Helpdesk.

LAQM Helpdesk
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