Local air quality management: policy guidance

Updated guidance for local authorities to take account of changes to industrial emissions legislation and requirements.

12: Air quality and energy

Combustion activities

12.1 Sources of air pollution from smaller scale combustion activities are becoming increasingly important when considering local air quality. Combustion plant are used for a wide variety of applications (such as electricity generation, domestic/residential heating and cooling, providing heat/steam for industrial processes, etc.) and can be a significant source of air pollutants (primarily oxides of nitrogen ( NO x), particulate matter ( PM) and sulphur dioxide ( SO 2)). The impact of combustion plant on air quality will depend on the location of the plant, the fuel type, how the plant is operated and the rate of emission of pollutants.

12.2 SEPA currently regulates combustion plant through the Pollution Prevention and Control (Scotland) Regulations 2012 (as amended) ( PPC) [45] . PPC Part A applies where the aggregated combustion capacity has a rated thermal input of equal to, or greater, than 50 megawatts ( MW) and controls emissions to all media. PPC Part B applies where a single appliance has a rated thermal input of between 20 MW and 50 MW and only controls emissions to air.

12.3 The Medium Combustion Plant Directive ( MCPD) [46] has recently been transposed into domestic legislation via the Pollution Prevention and Control (Scotland) Amendment Regulations 2017 [47] . This requires that new combustion plant with a net-rated thermal input of between 1 and 50 MW coming into operation after 20 December 2018 be registered/permitted by SEPA and may require them to meet specified emission limits, depending on the operating hours, size, type of fuel used, etc. Combustion plant that is put into operation before December 2018 will also have to register and meet emission limits but at a later date (either 2024 or 2029 depending upon the size of the unit(s)). Examples of these combustion plant include diesel generators for Short-term Operating Reserve ( STOR), biomass plant operating under the Renewable Heat Incentive ( RHI) and Combined Heat and Power Plant ( CHP).

12.4 At this time, many smaller combustion plant fall outside the PPC system and are currently regulated by local authorities under the Clean Air Act 1993 ( CAA). SEPA currently has no controls under the terms of the Clean Air Act and smaller-scale combustion activities will therefore remain under local authority control until such time as they enter PPC. More information on the Clean Air Act is contained in Section 12.18.

12.5 It is therefore important from a LAQM perspective that smaller scale combustion plant are appropriately screened for air quality impacts by the local authority at the planning stage, particularly if located in urban areas where sensitive receptors are present (such as schools, hospitals and care homes) or where there may be existing concerns over air quality. SEPA should also be consulted at the planning stage to ensure that smaller combustion plant which will in the future fall under the provisions of the MCPD can be identified, assessed for impact on air quality and brought into regulation at the appropriate time.

Air quality and biomass

12.6 The Scottish Government encourages the adoption of biomass combustion in order to reduce greenhouse gas emissions, mitigate against climate change effects and improve energy security and rural development. However biomass combustion contributes to emissions of air pollutants that are potentially harmful to human health, especially particulate matter. Concerns have thus been raised at the possible widespread adoption of biomass in urban areas with existing air quality issues.

12.7 The Scottish Government's 2020 Routemap for Renewable Energy in Scotland [48] sets out the Government's policy on all aspects of renewable energy development, including biomass. The use of biomass to generate energy should not have a detrimental impact on air quality, particularly where this would significantly affect public health or compromise the ability to meet legal obligations under air quality legislation. However, the Scottish Government recognises that renewable heat technologies can benefit air quality in situations where they replace oil and coal heating.

Biomass impact on air quality in urban areas

12.8 A research project was undertaken by the Scottish Government in 2008 [49] , which looked at emissions of PM 10 and PM 2.5 from wood burning biomass boilers. Detailed measurements were made of particulate emissions from a range of typical small scale biomass boilers installed and operational in urban areas throughout Scotland. Additionally, the potential cumulative impact of biomass boilers on particles concentrations in urban areas was evaluated, using Dundee and Edinburgh as case studies.

12.9 The study demonstrated that biomass boilers will not be the major source of PM 10 or PM 2.5 in urban areas. However, in areas that are already close to the 2010 PM 10 objective, the additional contribution of biomass may lead to exceedences at some urban background locations. Higher concentrations may be seen in areas close to specific sources. The study also shows that large scale uptake of biomass in urban areas could increase the difficulty in achieving the PM 2.5 exposure reduction target of 15% by 2020 in urban background areas. Since this study has been completed Scotland has also adopted a revised air quality objective for PM 2.5 of 10 µg m -3 (annual mean) to be met no later than 2020 and biomass combustion may have an impact on meeting this objective within the timescale.

Biomass and planning applications

12.10 As part of the study, screening tools have been developed to help local authorities assess the impact of both individual and multiple boiler applications. The revised technical guidance TG (16) contains updated guidance on assessing biomass impacts across the UK. The Scottish screening tools build on this and are designed to take account of the more stringent particles objectives in Scotland.

12.11 The individual installation tool will allow authorities to make informed judgements on the impact of biomass combustion on air quality and the potential need to specify control measures. The combined tool will help to identify high density or industrial areas where single large district or community heating schemes may be more appropriate and have less impact on air quality than numerous individual small boilers. For example, at one large proposed housing development in Edinburgh, the study shows that use of a small number of centralised biomass boilers may contribute 0.5-1.0 µg m 3 to PM 10 and PM 2.5 concentrations, compared to 2.0-5.0 µg m 3 for individual heating systems.

12.12 When considering planning applications for biomass boilers, local authorities should as a first step apply the new screening tools to assess the possible impact. If this assessment indicates that any individual boiler, or group of boilers in a specific area, has the potential to contribute to an exceedence of the PM 10 objectives, the local authority should give careful consideration as to whether the application should be approved.

12.13 Whilst determination of a planning application is a matter for the local planning authority, taking all relevant considerations into account, attention is drawn to chapter 11 of this guidance on air quality and planning, and to the letter sent by the Chief Planner to all local authorities in 2004 confirming that air quality is capable of being a material planning consideration. The impact on ambient air quality is likely to be especially important where:

  • the proposed development is inside or adjacent to an AQMA;
  • the development could result in designation of a new AQMA; and
  • the granting of planning permission would conflict with, or render unworkable, elements of a local authority's air quality action plan.

Biomass and air quality policy co-ordination

12.14 In 2012, the then Minister for Environment and Climate Change wrote to the Chief Executive of COSLA setting out the Scottish Government's policy position on air quality and biomass [50] . The information set out in this letter should also be taken into account by local authorities when considering biomass related planning applications. Useful information can also be found in Biomass and Air Quality Guidance for Scottish Local Authorities published by Environmental Protection UK in 2010 [51] , and in a guidance note published by the Scottish Government and Forestry Commission Scotland in 2015 [52] .

12.15 Use of abatement technology can reduce PM 10 and PM 2.5 emissions and, depending on the nature of the development and the type of boiler and abatement equipment, may help to ensure that there is no significant contribution to overall particles concentrations from a development or group of developments. Most larger new automatic boilers are fitted with some kind of flue gas cleaning device. Smaller boilers are generally not fitted with such devices and thus appropriate equipment will need to be identified. Ideally, any abatement technology chosen should have undergone some form of independent and generally recognised testing to ensure that it will have the desired effect.

12.16 Emissions can also be reduced by controlling stack heights. The Scottish Government's study suggests that a stack height sufficient to limit the individual ground level contributions to annual mean concentrations from each boiler to less than 1 µg m 3 is likely in most cases to protect public health without requiring excessive stack heights. Other features such as boiler design, specification, efficiency, fuel type, fuel quality and the suitability of the boiler to match the fuel load applied at the site should also be taken into account when considering the acceptability of proposals.

12.17 If, after taking all relevant considerations into account, a local authority decides to grant planning permission to a boiler in an area where air quality objectives are likely to be exceeded, or in other areas where human health may be significantly affected, it is strongly recommended that some form of mitigation - whether through abatement technology, appropriate stack height, specific system design features or a combination of these - is included in a planning condition to minimise the impact of such developments.

Clean Air Act

12.18 The Clean Air Act regulates emissions from commercial and domestic premises in Smoke Control Areas ( SCAs). However, this legislation was developed in the 1960s, primarily aimed at coal combustion, and is not appropriate for the current pollution situation and control of fine particulate or NO 2 emissions. Of specific concern is the fact that most existing boilers in urban areas are now gas fuelled and hence emissions are significantly lower than the Act's requirements. Therefore although boilers or combustion plant may meet Clean Air Act standards, in many circumstances they still have the potential to produce PM 10, PM 2.5 and NO 2 emissions that are worse than the current gas equivalent.

12.19 At the time of writing, a comprehensive review of the Clean Air Act was underway. This process commenced at the start of 2013 with a questionnaire circulated to local authorities, industry and other interested parties seeking views on how the Act should be revamped, and information on evidence gaps. The questionnaire responses were used as the basis for a focus group workshop run by Defra, which was followed later in 2013 by a call for evidence seeking additional input. This material is being used as the basis for reviewing the Act, which currently has an undefined timescale.

12.20 In advance of the main review of the Act, sections 20 and 21 have been amended to remove the need for authorised fuels and exempt appliances to be notified by Statutory Instrument. Instead, this has become an administrative procedure which will make the notification process much quicker and more efficient, and will result in a significant resource saving. These amendments were made through the Regulatory Reform (Scotland) Act 2014. The Scottish Government, in partnership with the other UK administrations, has developed an online notification system for authorised fuels and exempt appliances.


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