Biomass Boiler Air Quality Assessment
Specialist air quality consultants for biomass boilers and energy centres across the UK. NOx and PM emissions modelling, MCPD compliance, D1 stack height calculations and Environment Agency permitting support — by chartered environmentalists.
Biomass: The Most Scrutinised Combustion Plant in UK Planning
Biomass combustion has been promoted as a low-carbon heating solution under the Renewable Heat Incentive and successor schemes, but it is also the most heavily scrutinised type of combustion plant in UK planning. Wood-fired boilers emit nitrogen dioxide (NOx), particulate matter (PM10 and PM2.5) and carbon monoxide at rates per kWh many times higher than equivalent gas plant. In urban areas, in AQMAs and across Greater London, that combination puts biomass at the centre of LPA and statutory consultee attention — and means a robust air quality assessment is essential.
For any biomass installation above 1 MW thermal input the Medium Combustion Plant Directive (MCPD) applies. New plant (registered after 20 December 2018) must meet stricter ELVs for NOx, dust and SO2 than existing plant. Plant between 1 and 20 MW are typically permitted by the local authority; plant of 20–50 MW are permitted by the Environment Agency. Permits require commissioning monitoring, periodic stack testing and clear evidence of compliance with the EU/UK MCPD ELVs.
Stack height is determined by Defra HMIP Technical Guidance Note D1, supplemented by ADMS dispersion modelling. For larger plant we model NOx, PM10 and PM2.5 at all relevant sensitive receptors and present results clearly against the UK AQS Objectives, the AQAL/EAL framework and (in London) the GLA's biomass benchmarks. Abatement — cyclones, bag filters, SNCR or SCR for NOx control — is appraised where required to demonstrate that residual emissions are acceptable.
Malcolm Pounder CEnv MIAQM leads our biomass work. We are honest about what is feasible: if biomass simply isn't going to work for your site, we will tell you so before you spend money on a planning submission that the LPA will refuse.
Our Biomass AQA Services
Whether you're installing a 200 kW boiler in a school or a 25 MW energy centre on a campus, we have the depth to deliver.
Planning AQA for Biomass
Operational-phase air quality assessment for the planning application, covering NOx, PM10 and PM2.5 emissions modelled with ADMS dispersion software, results presented at all relevant sensitive receptors, and significance evaluation against IAQM 2017 criteria and the UK AQS objectives.
D1 Stack Height Calculation
Defra HMIP Technical Guidance Note D1 "guide" and detailed stack height calculations for NOx and PM, supplemented by ADMS dispersion modelling to confirm that the proposed stack height adequately disperses emissions. Optimised to meet planning and amenity constraints (visual impact, height limits).
MCPD Permit Support
Technical input to Medium Combustion Plant Directive permit applications, including emissions inventory, abatement specification (cyclones, bag filters, SNCR/SCR), stack testing plan, and compliance demonstration against the ELVs. We work alongside your operations and engineering teams.
GLA Biomass Benchmark Assessment
For schemes in Greater London, demonstration of compliance with the GLA's biomass NOx and PM benchmarks set out in the London Plan and Energy Hierarchy. Where biomass is genuinely unsuitable, we provide an honest assessment and can support comparison with heat-pump, gas CHP and district-heating alternatives.
Common Biomass Project Types
We work with developers, energy consultants, district-heating scheme operators, manufacturers and FM contractors. Most biomass projects fall into one of the categories opposite.
For each scheme we tell you honestly what level of evidence the LPA needs — sometimes a single-page screening note is enough, sometimes a full EIA-grade chapter is needed.
- Estate/farm biomass heating
- School and college biomass
- Hospital and care home plant
- Hotel and leisure biomass
- Commercial energy centres
- District heating networks
- Greenhouse/horticultural biomass
- Industrial process biomass
Frequently Asked Questions
Do biomass boilers need an air quality assessment?
Almost always, yes. Biomass boilers emit nitrogen dioxide, particulate matter (PM10 and PM2.5) and carbon monoxide at significantly higher rates per kWh than gas-fired plant, and most planning authorities — particularly in or near AQMAs and in Greater London — require an air quality assessment for any biomass installation above around 50–100 kW. For Medium Combustion Plant (1–50 MW thermal input) an MCPD permit is also required from the Environment Agency or the local authority depending on size.
What is the MCPD?
The Medium Combustion Plant Directive (MCPD), implemented in the UK through the Environmental Permitting Regulations, applies emission limit values (ELVs) to combustion plant with rated thermal input between 1 MW and 50 MW. For biomass plant the ELVs cover NOx, dust (PM) and SO2. New plant (registered after 20 December 2018) have stricter ELVs than existing plant. Permits are issued by the EA (for plant over 20 MW or where the site is permitted under environmental permitting) or the local authority. Compliance is demonstrated through commissioning monitoring and periodic stack testing.
How is stack height calculated for a biomass boiler?
Stack height is determined using the Defra HMIP Technical Guidance Note D1 procedure ("Guidelines on Discharge Stack Heights for Polluting Emissions"). The D1 "guide" method gives a screening-level result; the detailed D1 procedure takes account of building wake effects, emission rate, terrain and nearby sensitive receptors. We then supplement the D1 calculation with ADMS dispersion modelling to demonstrate that predicted concentrations at sensitive receptors (residential properties, schools, hospitals, ecological sites) are well below the AQS objectives and Environmental Assessment Levels.
Can biomass plant be installed in an AQMA?
Yes, but it is heavily scrutinised. Most local authorities operate AQMA designations because of existing NO2 or PM exceedances, and any new significant emission source will be carefully assessed. In Greater London the GLA's biomass position is particularly restrictive: small biomass in residential applications is generally discouraged, and any biomass plant requires demonstration that emissions meet the GLA's stringent NOx and PM benchmarks. Each scheme is reviewed on its merits — we will tell you honestly whether biomass is appropriate for your site, or whether an alternative (heat pumps, gas CHP, district heating) would be a smoother route through planning.
What does a biomass AQA cost?
Fees depend on the size of plant, the number of modelled sources, the proximity to AQMAs and sensitive receptors, and whether the work needs to be packaged with a Medium Combustion Plant Directive (MCPD) permit application. We provide fixed-fee quotes following a brief initial conversation. Typical fees for a single-boiler AQA with ADMS dispersion modelling and a D1 stack height calculation are competitive with national consultancies — call us and we'll give you a same-working-day estimate.