Air Quality Modelling in ESME

Published: 9 June 2020

Air Quality Modelling in ESME explores scenarios for decarbonisation and air quality.

Exposure to outdoor air pollution is responsible for around 40,000 premature deaths each year in the UK, costing the economy £20 billion every year. Activities within the energy system are responsible for the majority of air quality (AQ) emissions.

Energy Systems Modelling Environment extends functionality to include air quality pollutants

With UK government committed to decarbonising the economy and improving air quality long term, it is imperative that strategies to support these two agendas are aligned. Without a ‘whole systems’ approach, there is potential for decarbonisation efforts to be in conflict with AQ measures. One example is the incentivising of diesel vehicles, which are more fuel-efficient and therefore lower in CO2, but result in higher levels of NOx emissions compared to petrol vehicles.

In this study, we have incorporated AQ pollutant emissions into Energy Systems Catapult’s Energy Systems Modelling Environment (ESME), to enable a whole systems scenarios to be modelled for decarbonisation and clean air. ESME is used to inform energy policy, innovation spending and other strategic analysis. Now, it can be used to systematically explore the wide range of co-benefits and trade-offs between these two agendas, including at a regional and local scale.

Air Pollution Modelling: Key points

Emissions factors for ESME were derived from the National Atmospheric Emissions Inventory (NAEI), and a detailed calibration exercise undertaken to ensure consistency with the current inventory. Damage costs associated with each pollutant were derived from DEFRA datasets.

  • Decarbonisation does deliver a reduction in AQ emissions, but this falls short of official, legally binding targets in the National Emissions Ceilings Directive.

Achieving these targets by imposing fixed emissions ceilings relies upon significant changes to the energy system design. This is largely because reductions in AQ emissions in ESME can only be achieved by switching to (often radically) low carbon technologies, when in reality small adjustments to existing technologies (e.g. for clean-up of tailpipe emissions) may be sufficient to deliver near-term AQ targets. The inclusion of AQ-abatement options in ESME would provide further critical insight.

  • ESME modelling system scenarios show the damage costs associated with AQ emissions drive regional differences in decarbonisation pathways. The model indicates that the most cost-effective scenarios for urban air quality in areas such as London should see earlier, and deeper decarbonisation of the transport sector compared to rural regions as a result of damage costs associated with NOx and PM2.5 emissions prompting a shift to electrification.

In other regions, damage costs lead to a switch to petrol vehicles from diesel to reduce NOx and PM with the trade-off being an increase in CO2 emissions as a result of engine efficiency.

  • Strict adherence to AQ emissions ceilings can deliver deeper decarbonisation in the near term. If AQ emissions ceilings are enforced, then national CO2 emissions in the 2020s and 30s fall below the carbon budgets due to increased renewables and nuclear power alongside CCGTs shifting to peak operation from baseload provision of electricity.
  • Early phase out of non-Renewable Heat Incentive compliant biomass boilers is required to meet near term AQ targets. Modelling suggests an early phase out of non-RHI compliant burners/boilers given their impact on air quality. Further analysis is needed to explore the precise role and impact of biomass for heat, including a risk assessment of different proportions of compliant/non-compliant fuels and burners in the system.
  • Brake, tyre and road surface wear are important sources of PM2.5 emissions, which remain even in a decarbonised transport system. Further reductions in particulate matter (PM) could be delivered through reduced demand for car travel, including switches to other modes such as walking, cycling or public transport. At the same time, alternative braking systems and other innovations that reduce PM emissions from brake, tyre and road surface wear would be of value as the transport system continues to decarbonise.

Note: The analysis in this report was commissioned by BEIS and conducted between December 2018 and July 2019 in an 80% emissions context.

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