Reducing greenhouse gas (GHG) emissions and improving air quality are closely linked objectives but are not considered simultaneously under current policy frameworks. In this blog, Professor Grant Allen discusses the benefits of developing a common policy framework aligning GHGs reduction goals with improvements in air quality. Considering these two objectives simultaneously, rather than in isolation, can improve policy outcomes.

• Policies targeting GHG reductions also improve air quality and vice versa, highlighting the need for joined-up policymaking.
• Joined-up thinking and cross-departmental discussions between Defra and BEIS can reduce counterproductive policy impacts, and accelerate progress towards net-zero goals and air quality improvements.

The core objectives of reducing greenhouse gas (GHG) emissions and improving air quality are very closely linked. Changes in either are often directly related to the other as their main causes are typically the same. For example, petrol vehicles are a source of CO2 (a greenhouse gas), as well as a source of pollutants affecting air quality such as volatile organic compounds (VOCs) and particulate matter, whilst diesel cars are also a source of NOx – a pollutant known to adversely affect health which the UK government is legally committed to reducing. Co-emission of GHGs and pollutants affecting air quality is typical for any combustion source, including moorland fires. Improving air quality and reducing greenhouse gas emissions are often (but not always) co-benefits of each other. Aligning these two objectives more closely in terms of policy and regulation may result in much improved outcomes.

In the UK, greenhouse gas emissions policy is broadly within the remit of BEIS, whereas air quality policy is within the remit of Defra. Although BEIS and Defra coordinate advice on GHG emissions reporting, currently the two departments do not formally coordinate on air quality and neither co-considers the policy impacts of both air quality and GHG emission. This division is unnecessary and problematic. There is a definite need for joined-up policymaking: cross-fertilisation of interdepartmental and regulatory expertise could help simultaneously tackle these mutually and directly related objectives in an aligned framework.

Emissions flux vs Concentration thresholds

The UK has committed to an ambitious and world-leading Net Zero agenda by 2050. The focus of policy in this context is on “fluxes” of greenhouse gases – the net annual carbon-equivalent mass emitted and sequestered nationally. Natural ecosystem services (carbon sinks), targeted interventions on industrial activity-related emissions, and carbon capture and storage are all important terms in achieving this national net zero sum. Policies that reduce GHG emissions will invariably lead to improvements in air quality and vice versa, but these co-benefits are not currently co-considered and quantified. The planned electrification of the UK vehicle fleet and phase-out of new petrol and diesel cars by 2030 is an obvious co-benefit, as might be a transition from natural gas to hydrogen. However, residual air quality impacts may remain, such as particulate matter associated with brake and tyre wear.

There is a subtle difference in the approach to policymaking for air quality improvement. Air quality policy focuses on ambient concentration thresholds rather than emission fluxes, by virtue of proven health impacts at elevated concentrations of pollutants, especially in urban environments. Flux and concentration of any atmospheric pollutant are intimately linked – related directly as a function of chemistry and dispersion in the atmosphere. Put simply, reducing fluxes can reduce pollutant concentrations. The current focus on meeting air quality concentration thresholds has led to policy interventions at local level. These include managing traffic flow, road design and siting of industry, to maximise pollutant dispersion and minimise local concentrations. However, these measures don’t explicitly consider emission fluxes, or seek to minimise the primary sources of pollution.

Lessons from the diesel car scandal

To maximise the co-benefits of GHG emissions reduction and air quality improvement, we should develop a common policy framework that takes into account minimising fluxes of both GHGs and air pollutants, and not solely minimising pollutant concentrations. Considering both objectives simultaneously could optimise policy efficiency and outcomes. However, when either is considered in complete isolation, the other could fail spectacularly.

A prescient example of this is the diesel car scandal, representing a failure of Government policy to recognise the significant impact of increased NOx emissions from otherwise less carbon-intensive diesel cars. A prioritised drive to reduce carbon emissions led to active policies to promote diesel cars over petrol, including subsidies to purchase them. Although diesel cars do emit less CO2 per mile of travel, they also emit NOx, unlike petrol vehicles. This policy has undoubtedly contributed to poorer urban air quality since it was introduced and will now take time to reverse, affecting the health of exposed populations in the meantime. A further pressing example is the current rise in popularity of domestic wood-burning stoves. Wood is considered a carbon-neutral fuel source, so this can reduce household carbon footprints if used for heating instead of gas or electricity. However, wood burning can also be a major source of particulate pollution.

Problems also arise if only air quality concentrations are considered and not fluxes of pollutants. For example, an efficient way to reduce local urban air pollutant concentrations may be to divert vehicles over many additional miles, dispersing emissions away from local hotspots. Clearly, such an approach may lead to an increase in the CO2 emitted due to the additional miles travelled. These contrasting examples illustrate the continuing real-world effects of a lack of a policy prioritisation framework for GHGs and air quality. There is a clear need for more joined-up thinking in government to prevent local and national policies from working against each other and achieve optimal outcomes for both air quality and GHG emission reduction.

A call for joined-up thinking

At present, the UK has no policy framework that co-considers GHG emissions and air pollutant concentrations in planning regulations. Reduction of GHG flux represents a systemic threat to the planet as a whole, whereas elevated air pollutant concentrations represent a local health threat to exposed populations. It is clearly challenging, but vitally important to decide how such issues should be prioritised in policy. These two environmental aspects are not mutually exclusive – quite the opposite. There is scope to maximise the co-benefits of net-zero and air quality, but only if both are considered simultaneously, examined from a viewpoint of emitted flux and weighted (then prioritised) by their respective impacts.

Having an interdepartmental disconnect on air quality and GHG emissions can result in counteracting and counterproductive policy, as exemplified by past failures concerning diesel cars. Collaborative discussion of such a policy framework should be a priority for BEIS and Defra, ideally resulting in new guidance to planning agencies and regulators so that optimal outcomes on both air quality and GHG emissions can be achieved. Leadership and coordination of such an initiative may well reside more naturally within Defra currently, but with an established cross-departmental group to ensure joined-up thinking. In addition, the UK regulatory framework should draw on the example of the US Environmental Protection Agency, which has regulatory oversight of both GHG emissions targets and air quality, in a way that the UK Environment Agency currently does not.

This article was originally published in On Air Quality, a collection of thought leadership pieces and expert analysis on how to tackle air pollution, published by Policy@Manchester.

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