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Roadside NO2 Projection Factors


The table below provides the year adjustment factors for roadside NO2 concentrations, with different factors for London (Central, Inner and Outer) and the rest of the UK. The adjustment factors can be used to estimate the annual mean NO2 concentration in future years from current monitoring data. The factors have been calculated as the average of modelled concentrations across approximately 1,900 road links in London, and 7,000 links elsewhere, taking into account the changes in traffic activity, and emission factors for NOx and primary NO2 (f-NO2). The number represents the adjustment factor to be applied.

Worked Example

The measured NO2 concentration at a roadside site in Outer London in 2019 is 44.5µg/m3. The projected concentration for 2021 would be:

2019 NO2 Concentration x (Outer London 2021 NO2 Projection Factor / Outer London 2019 NO2 Projection Factor)

44.5 x (0.829/0.945) = 39.0µg/m3

See para 7.75 of Technical Guidance LAQM.TG(22) for more information.

Current Version

Roadside NO2 Projection Factors
Year Central London Inner London Outer London Rest of UK
(HDV = <10%)
Rest of UK
(HDV >10%)
2018 1.000 1.000 1.000 1.000 1.000
2019 0.813 0.909 0.945 0.953 0.942
2020 0.766 0.811 0.878 0.906 0.889
2021 0.740 0.767 0.829 0.855 0.835
2022 0.715 0.727 0.775 0.807 0.785
2023 0.696 0.693 0.738 0.765 0.743
2024 0.676 0.661 0.695 0.724 0.703
2025 0.660 0.634 0.657 0.686 0.667
2026 0.652 0.616 0.630 0.653 0.637
2027 0.645 0.598 0.606 0.622 0.610
2028 0.638 0.580 0.582 0.595 0.587
2029 0.632 0.563 0.560 0.571 0.566
2030 0.626 0.546 0.542 0.550 0.549


HDVs include HGVs and Buses.

HDV emission projections for NO2 are expected to decline at a different rate to other vehicle types, i.e. cars and vans.

The projection factors for Central London include the impact of the Ultra Low Emissions Zone (ULEZ) from 2019 onwards.

The column “Rest of UK (HDV >10%)” is appropriate for roads outside London where HDVs contribute greater than 10% of the total traffic flow. It is expected that the majority of roads that fall into this category will be motorways or trunk roads.

For roads outside of London that have less than 10% HDVs (including any motorways or trunk roads with less than 10% HDVs), it is recommended that the “Rest of UK (HDV =<10%)” factors are used, which represent the anticipated changes in ambient NO2 concentrations along these roads, where cars and vans have a greater influence on future emission projections.

For roads outside of London where traffic fleet break down information is not known and it is not possible to undertake a bespoke traffic survey within the required timescales, it is recommended that a precautionary approach be taken whereby the “Rest of UK (HDV =<10%)” projection factors are used.

Roadside locations are typically within 1 to 5 metres of the kerbside, but may extend up to 15 metres depending upon the road configuration and traffic flow.

The table is expected to be updated from time to time and therefore is not provided within LAQM.TG(22) to enable these amends to take place.

For further support, or to request a PDF copy of the table, please contact the LAQM Helpdesk.

LAQM Helpdesk
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