How do I assess road traffic emissions of ammonia?
Emissions of ammonia increasingly occur as a byproduct from NOx abatement measures (catalytic converters or Selective Catalytic Reduction) in petrol and diesel vehicles. There is consequently an increasing requirement to consider emissions of ammonia when undertaking assessments which impact road traffic numbers close to sensitive ecological receptors or designated ecological sites.
As ammonia is not a relevant pollutant under the Local Air Quality Management (LAQM) framework, the LAQM Technical Guidance (TG22) does not provide detailed guidance on how the pollutant should be assessed. Additionally, the LAQM tools such as the Emissions Factors Toolkit do not currently provide an option to output emissions of ammonia.
Whilst Defra cannot yet make specific endorsements or recommendations, should practitioners need to undertake assessment of ammonia from road traffic sources, there are a number of notable reports and resources detailed below which may be useful:
- National Highways have devised a method of assessing the ammonia impacts from traffic schemes based on the ratio between emissions factors for NOx and NH3 provided by the National Atmospheric Emissions Inventory. This model is not publicly available but further detail on the method can be found in the air quality Environmental Statement chapter (Para 5.3.100-106) which informed the examination of the Lower Thames Crossing Development Consent Order application.
- Air Quality Consultants have produced an emissions tool (Calculator for Road Emissions of Ammonia (CREAM)) which provides link specific ammonia emissions outputs from traffic data inputs in a similar format to Defra’s Emissions Factors Toolkit. The tool is available alongside a report which discusses the importance of traffic related ammonia emissions (Ammonia Emissions from Roads for Assessing Impacts of Nitrogen-sensitive Habitats).
- The EMEP/EEA air pollutant emission inventory guidebook provides details on the calculation of ammonia emissions from road transport sources in chapters A.3.b.i-iv and 1.A.3.b.i-iv Appendix 4. The EMEP/EEA guidebook is the source of other emission factors used by Defra’s Emissions Factors Toolkit for calculating road traffic emissions from NOx, PM and CO2.
It is recommended that once practitioners are clear how they wish to undertake their assessment of ammonia impacts from road traffic, they confirm their approach with Natural England consultations@naturalengland.org.uk. Information on Natural England’s Discretionary Advice Service is found here. Natural England will not comment specifically on the suitability of the model selected, as it is not within their remit to review or endorse models. However, they require that the approach selected addresses all pollutants, including NOx, ammonia and nitrogen and acid deposition, and other pollutants where relevant, both alone and in combination with other plans and projects (including non-road projects).
Development of Guidance and Tools for Ammonia Assessment
To assist in a standard method of assessment of ammonia emissions from road traffic in future, Defra and Natural England are currently looking to undertake a study considering the different approaches that are being used. It is hoped that the outputs of this study would enable guidance documents and tools for the assessment of ammonia emissions from road vehicles to be made available through Defra or Natural England in future.
