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FAQ 5 – Local Air Quality Trends

Measured nitrogen oxides (NOx) and/or nitrogen dioxide (NO2) concentrations in my local authority area do not appear to be declining in line with national forecasts. Should I take this into account in my Review and Assessment work?

Defra and the devolved administrations have published Year Adjustment Factors for roadside NO2 concentrations, and Background Maps for NOx and NO2 concentrations for all years up until 2030. Technical Guidance LAQM.TG(22) advises local authorities to use this information to adjust measured concentrations to future years (e.g. annual mean NO2 concentrations measured in 2020 can be projected forwards to 2025). Background maps for future years are also used to support detailed modelling studies for Review and Assessment.

These projections are based on the Pollution Climate Mapping (PCM) Model studies carried out on behalf of Defra and the devolved administrations. The PCM model is a collection of models designed to fulfil part of the Air Quality Standards Regulations 2010 requirements to report on the concentrations of particular pollutants in the atmosphere. It is used to provide background pollutant concentration outputs on a 1×1 km grid plus around 9,000 representative road side values. The projections take full account of current understanding of the expected changes in sector-based emissions up until 2030. They also take account of the expected changes to primary NO2 emissions.

For a variety of reasons, it is possible that local information identifies disparities between the measured concentrations and the projected decline in NOx and/or NO2 concentrations associated with the emissions forecasts. It is important that local authority Review and Assessment work takes into consideration any such disparities and gives due consideration to any local historical trends identified from ambient NOx and/or NO2 monitoring. Any other information available at the local level should also be considered, e.g. the potential impact of any committed developments.

Therefore, local authorities should take into account any local trends at either roadside or background locations and their expected effect on projected NOx and NO2 concentrations to ensure decision making based on such information is robust.

Should local authorities require further support to ensure local information is being taken into account appropriately in Review and Assessment work, then please contact the LAQM Helpdesk.

LAQM Helpdesk
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