Local air quality management: policy guidance

5. Air quality assessment following AQMA declaration

5.1 Overview

Once an AQMA has been declared, an assessment to provide the technical justification for the measures an authority intends to include in its action plan will normally be required. This will allow authorities to:

• Calculate more accurately how much of an improvement in air quality will be needed to achieve the air quality objectives within the shortest possible time in the AQMA.
• Refine their knowledge of the sources and their contributions to pollution so that air quality action plans can be properly targeted.
• Take account of national policy developments which may come to light after the AQMA declaration.
• Take account as far as possible of any local policy developments which are likely to affect air quality and which were not fully factored into earlier assessments. These might include, for example, changes to national or local planning policy, the implications of any new transport schemes that are likely to be implemented in or close to the AQMA, or of any new major housing or commercial developments.
• Carry out new or additional real time monitoring.
• Respond to any comments made by statutory consultees on any aspect of the AQMA declaration process, particularly where these have highlighted that insufficient attention has been paid to, for example, the validation of modelled data.

In many cases, authorities will already have done some of the necessary work as part of routine review and assessment or specific studies undertaken to inform AQMA declaration. They may already have a reasonably clear idea of which sources are responsible for the air quality problem and may already have calculated how much of an emissions reduction from each source would be necessary to achieve compliance with the objectives of concern. In these cases, relatively little additional work will be required, although authorities will still be required to show that they have considered the possible impact on the AQMA of subsequent local and national developments.

This assessment work should be taken forward in parallel with the development of the action plan, allowing authorities to model the likely effects of particular policy measures, such as the introduction of a LEZ or other traffic management schemes. As well as modelling the impact of particular measures on emissions and ambient air quality, authorities should also show that they have given due consideration to their likely costs and benefits and timescales for implementation and completion of measures. The assessment should demonstrate that authorities have considered a range of options and chosen the most cost-effective solutions to achieve the air quality objectives within the shortest possible time.

5.2 National Low Emission Framework (NLEF)

Local authorities that have declared AQMAs should have regard to the NLEF when developing their air quality action plans. The NLEF^[10] is intended to support and complement the existing LAQM system and assist local authorities to determine whether a LEZ is appropriate to address air quality issues in their area.

The NLEF process will be undertaken by all local authorities with a newly declared AQMA or where circumstances have changed substantially in an existing AQMA and where transport emissions are the primary reason for declaration. Results of the NLEF screening and, where appropriate, assessment processes will be reported in the APR.

5.3 Calculating how much of an improvement is necessary inside an AQMA

A local authority must also show that it has calculated the reduction in emissions required to achieve the objective/s of concern within the shortest possible time. Having done this, the authority will be better placed to consider whether the measures proposed to achieve these reductions are proportionate and cost effective. It is important to note that a reduction of 10% in total emissions will not necessarily result in a 10% improvement in ambient air quality, because this fails to take account of background concentrations and also the complex atmospheric chemistry involved in, for example, the conversion of NO_x to NO₂.

5.4 Source apportionment

One of the most important elements of the technical assessment is the consideration of the extent to which different sources contribute to the problem. For example:

• Is road transport entirely to blame for the exceedance of an NO₂ objective, or is there a significant contribution from an industrial/other commercial source?
• To what extent do other sources contribute (for example, aircraft or train movements)?
• Within the road transport sector, to what extent are different classes of vehicle responsible for the emissions?
• Does the traffic in the whole urban area contribute more to the exceedance than the nearby road?
• Are sources outside the authority’s immediate area contributing to any significant extent?

Only when an authority has a reasonably clear idea of the total breakdown of emissions from all sources can it draw up an appropriately targeted action plan. It will not always be possible to do this with absolute precision, and variabilities in between year meteorological conditions will also have an effect on the relative contribution from different sources (including background or transboundary contributions). Authorities must show that they have calculated, in percentage terms, the extent to which different sources are responsible for any forecast exceedances. This will allow consultees to form a view on whether the action plan is proportionate, properly targeted and fit for purpose.

If a source over which an authority has little control (dual carriageways and motorways) is responsible for a significant percentage of local emissions, an authority should not demand disproportionate emissions reductions from other sources in pursuit of the objectives. Instead, it should note in its action plan that it has done all it reasonably can to bring about reasonable and proportionate emissions reductions from those sources over which it has any influence, but that further emissions reductions are required from other sources before the objectives can be achieved. The action planning section describes how local authorities should engage with other organisations who may be responsible for providing additional emission reduction measures which are required to help work towards meeting the objectives.

5.5 Taking account of policy changes

In many cases, central government policy developments may affect the designation of an AQMA or the extent to which local actions are necessary to achieve the prescribed air quality objectives. Possible examples include:

• Changes to nationally prescribed air quality objectives, which may themselves reflect changes to European Union (EU) limit values or World Health Organisation (WHO) Guideline Values.
• Scientific and technical developments, such as changes to the emissions factors to be used in certain calculations.
• Major policy developments such as those encouraging take up of renewable energy or new planning policies.
• The introduction of new powers for local authorities.
• Measures to promote the use of cleaner fuels/ low emission vehicles which might affect the composition of the total vehicle fleet by the compliance date.
• Decisions on local development, such as the location of a new residential development.
• Developments in the industrial pollution control framework.

5.6 Further monitoring

In many cases, local authorities will have based their AQMA designation on the results of a relatively short monitoring period, or entirely on the results of their modelling. In practice, even where at least twelve months' worth of monitoring data were available at the time of designation, there may still be uncertainties associated with the results (were the meteorological conditions typical, for example). Sometimes, authorities will have diffusion tube data covering a long period, but only a limited set of results from a continuous monitor. Local authorities may therefore wish to carry out additional monitoring at key points to validate earlier findings and/or commit to ongoing monitoring as part of the action plan. Low-cost sensors have an important role to play in this process and further information can be found in LAQM. TG (22).

Following on from this, the designation of an AQMA will often have been based on a large number of assumptions (such as that traffic flows along a particular road are at a particular level). Additional assessment during action plan preparation is an opportunity to test these assumptions, in order to ensure that they are as accurate as possible.

5.7 Costs and benefits

A key element of the action plan will be an estimate of the costs, benefits and feasibility of different abatement options to allow for the development of proportionate and effective measures. The cost benefit analysis should cover both health and environmental considerations, besides the financial cost of any measures for the local authority and other affected parties. The options selected for taking forward in the plan should be reported on in action plan progress reports as part of the APR process.