Pathway to WHO: achieving clean air in the UK

Modelling air quality costs and benefits

Background

The UK Environment Bill is currently under consultation, with the intention of setting two targets for PM_2.5 for 2030, one related to meeting an annual average concentration everywhere where people may be exposed, and the second relating to population exposure reduction over time. Target setting in the Environment Bill refers to the World Health Organisation (WHO) guidelines, which are themselves set by considering the scientific evidence of the human health impacts of each pollutant, but without consideration of the practicality of meeting the target. The previous and long-standing WHO guideline value was set at an annual average of 10 μg m^-3, hereafter referred to as WHO-10, but during the project has been reduced to 5 μg m^-3 (WHO Global AQ Guidelines), with the original 10 μg m^-3 guideline value now considered to be an interim target. The new lower guideline value of 5 μg m^-3 reflects the increasing evidence of PM_2.5 health effects at very low concentrations.

Purpose

This report was funded by the Clean Air Fund (CAF) under the project ‘Pathway to WHO: achieving clean air in the UK’, with the intention of submitting the results as part of the UK Environment Bill consultation.

This report provides both a technical backup to the main CAF report, and addresses the questions of whether the UK can achieve the WHO-10 target by 2030, what requirements this places on UK policy makers, and whether the costs and benefits justify such action. Within this document we specifically answer the questions:

• Can the UK meet the WHO-10 interim target in 2030?

• What population exposure reduction can be achieved between 2018 and 2030?

• What are the health benefits associated with achieving the WHO PM_2.5 interim target?

• What are the monetary benefits and costs associated with achieving the WHO PM_2.5 interim target?

Can the UK meet the WHO-10 interim target in 2030?

UK PM_2.5 concentrations for UK2030+LS1 were forecast to be below the WHO-10 for a large proportion of the UK population. However, results showed that there were exceedences in London, close to roads and towards the city centre, as well as exceedences in other UK cities, again close to major roads.

Near to sites of industrial biomass burning, exceedences of WHO-10 occurred in 2030, although model sensitivity tests showed that this was likely to be a worst case prediction. These areas of high PM_2.5 were very local to the industrial sources and are often in locations away from large populations.

The London scenario LS2 was shown to be effective at further reducing PM_2.5 below WHO-10, with <1% of the area of London predicted to be above 10 μg m^-3. Scenario LS3 proved to have modest benefits over scenario LS2.  A detailed analysis of the kerbside concentrations along London’s major roads, showed that ~11% still risked having concentrations > 10 μg m^-3 for scenarios LS2 and LS3.

It is important to consider model uncertainty in interpreting the 2030 predictions. To do this we estimated a concentration below which we were 95% confident that the 2030 concentration would be below WHO-10. The concentrations were 7.9 μg m^-3 in the UK and 8.3 μg m^-3 in London.

Considering model uncertainty resulted in ~4% of the UK remaining at risk of exceeding WHO-10 (UK2030+LS1). Whilst this was a small percentage of the UK’s total area, it represented the large urban populations in the south east of England and cities such as Birmingham and Manchester. For scenario LS1 the proportion of London’s area at risk of exceeding the WHO-10 was 27% but for scenarios LS2 and LS3 was similar to the UK at ~4%.

Finally, recent measurements have shown that the impact of the COVID lockdown has resulted in compliance with WHO-10 in 2020 at all but a small number of sites in London.

What population exposure reduction can be achieved between 2018 and 2030?

Population Weighted Average Concentrations (PWAC), were calculated for all of the UK’s 382 local authorities. PWAC links air pollution concentrations with population data, so is more relevant to the air pollution to which people are exposed.

Between 2018 and 2030, PWACs for PM_2.5 were predicted to reduce by a range of -0.9 μg m^-3 (Scotland) to almost -4 μg m^-3 (inner London) and by ~-2 μg m^-3 for the UK. By region, between 2018 and 2030, the PWACs reduced by -2.3 μg m^-3 (-23%), -1.4 μg m^-3 (-20%), -0.9 μg m^-3 (-17%) and -1.7 μg m^-3 (-23%) in England, Northern Ireland, Scotland and Wales, respectively. The PWAC in London (Scenario LS2) was predicted to reduce more, by -3.3 μg m^-3 (-29%) overall; by -3.7 μg m^-3 (-31%) in Inner London and -3.0 μg m^-3 (-28%) in Outer London. Reductions in Greater Manchester and Glasgow City were -2.6 μg m^-3 (-24%) and -1.5 μg m^-3 (-20%), respectively.

When weighted by the number of people at risk, 41% of local authorities had PM_2.5 exposure levels above WHO-10 in 2018. This was predicted to fall to less than 1% by 2030 for scenario UK2030+LS1. Furthermore, the 2030 LS2 and LS3 forecasts show that all local authorities’ PWACs were under WHO-10 in 2030.

What are the health benefits associated with achieving the WHO PM_2.5 interim target?

The UK2030+LS1 scenario leads to 11.5 million life years gained across the UK population over the time period 2018–2134 compared with 2018 concentrations remaining unchanged. This calculation is for deaths from all causes including respiratory, lung cancer and cardiovascular deaths.

The result can also be expressed as an average gain in life expectancy of 8–9 weeks for the 745,000 children born in 2018, although this only reflects a small proportion (115,000 life years) of the overall gains in life years for children born in all the other years and for all the other age groups in 2018.  As this gain in life expectancy is an average, life-expectancy gains could potentially be larger across fewer people, with the remainder less affected.

Many of the life years gained in the UK2030+LS1 scenario are in cities, including 2 million life years in London, 630,000 in Manchester and 90,000 in Glasgow from 2018-2134.

The remaining policy scenarios only involve benefits in London as that is where the additional policies are concentrated.  There is predicted to be a gain of around 2.4 million life years for UK 2030+LS2 and around 2.5 million life years for UK 2030+LS3 compared with the 2 million life years for UK 2030+LS1 from 2018-2134. These figures are equivalent to a 28.5%, 29.3% and 24% reduction in life years lost respectively compared with 2018 concentrations remaining unchanged. Put another way, the additional policies in London in LS2 and LS3 add 0.4 and 0.5 million life years, respectively, to the life years gained under LS1.

The improvement in average life expectancy from birth in 2018 in London is around 2–2.5 months under UK2030+LS1, and 2.5–3 months for UK 2030+LS2 and LS3.

The gain in life years is the dominant part of the health benefits but other health outcomes were also calculated in a more approximate way.  These analyses also showed substantial health benefits from both the PM_2.5 reductions and from reductions in PM₁₀ and NO₂ that occurred as a consequence of the policies that reduced concentrations of PM_2.5.

The benefits from reductions in other health outcomes for the UK2030+LS1 scenario ranked by average numbers of cases per year from 2018-2030 was as follows:

• 388,000 fewer asthma symptom days in children
• 149,000 fewer adults with chronic phlegm
• 98,000 life years gained
• 25,000 fewer asthmatic children with bronchitic symptoms
• 13,000 fewer acute bronchitis infections in children
• 3,600 fewer respiratory hospital admissions
• 3,100 fewer new cases of coronary heart disease
• 2,700 fewer cardiovascular hospital admissions
• ~20 fewer infant deaths

Of course, these health outcomes vary in severity with new cases of coronary heart disease and respiratory/cardiovascular hospital admissions being more serious than symptoms.  In addition, the evidence and quantification methods are more established for outcomes such as hospital admissions than for infant deaths.

The equivalent numbers for the UK2030+LS2 scenario are given in the main report.  As for the gains in life years, there are improved absolute benefits for these two scenarios. The proportionate increase is relatively small (e.g. 2% fewer asthmatic symptom days in asthmatic children) because for the UK2030+LS2 scenario there are no additional UK policies and the LS1 policies have already contributed a substantial amount to air pollution reductions in London.

The additional benefits for the UK2030+LS3 scenario are only minor as a substantial reduction in wood burning has already occurred in the other scenarios and it is only one pollutant and policy addressed in this last scenario.  As only PM_2.5 concentrations change, the pattern of health outcomes contributing to the benefits is a bit different.  For example, with no changes in NO₂ concentrations there are no additional reductions in bronchitic symptoms in asthmatic children. 

What are the monetary benefits and costs associated with achieving the WHO PM_2.5 interim target?

This study uses economic valuation tools to estimate the impact of air pollution across four channels: premature mortality, morbidity, healthcare costs and impacts on the labour market. The total health and economic benefits of reducing air pollution in the UK are valued at £383 billion between 2018-2134, which justifies policies that cost up to this level. Avoiding premature mortality provides the largest benefit, valued at £218 billion, while reducing the level of illness in the population across the range of disease modelled provides benefits of £130 billion. Air pollution related illnesses can result in people taking time off work (absenteeism), or attending work but being less productive (presenteeism). Reducing air pollution related illnesses could add £27 billion by reducing workplace absences and improving productivity.

This study did not assess the costs of new policies analysed. A review of the cost-benefit analysis of key policies in the UK2030 scenario including the Industrial Emissions Directive, the Medium Combustion Plant Directive, transport policies, and regulations covering wood burning and coal show that the benefits are more than two times the costs of the policies. The benefit-cost ratios for policies covering the buildings sector are typically lower, but the benefits still outweigh the costs.

Policy impacts and recommendations

PM_2.5 results for scenario UK2030+LS1 demonstrated important air pollution benefits that will improve people’s health in the UK, reduce climate impacts and help achieve Net Zero commitments.

Source apportionment results for London have demonstrated that local emissions may contribute to PM_2.5 by up to ~4 μg m^-3, and that cooking, domestic wood burning and road traffic emissions were important. Finally, industrial biomass burning was an important albeit highly uncertain source of PM_2.5 UK wide.

Overall, the results for London demonstrate the benefits that may be achieved by local action and supports DEFRA’s plan to combine the benefits of UK emissions reductions with local authority action to reduce PM_2.5 exposure in their area.

For robust policy assessment there is a need to reduce model uncertainty, and that PM emissions sources such as vehicle non-exhaust, domestic wood burning and cooking are likely to be important in achieving this.

A more comprehensive assessment of wood burning in industry is needed as none of the industrial biomass burning sources identified in the National Atmospheric Emissions Inventory was supported by local PM_2.5 measurements.

Authors: David Dajnak, Nutthida Kitwiroon, Nosha Assareh, Gregor Stewart, Dimitris Evangelopoulos, Dylan Wood, Heather Walton and Sean Beevers