Cleaner Air for Scotland strategy: independent review

Conclusions and recommendations from the independent review of the Cleaner Air for Scotland strategy.

5. Health and Environment


5.1 The Health and Environment Working Group[21] produced initial analysis and recommendations for consideration by the Steering Group for this section of the report[22]. The report reflects discussions on evidence relating to the health impacts of air pollution in Scotland by members of the 2019 CAFS Review, Health and Environment Working Group and issues identified by the Steering Group. Some differences, of evidence, interpretation and opinion emerged on some topics, including around the philosophy of precaution versus compelling evidence on causation and on how to address scientific uncertainty associated with variation in local and international evidence on some health impacts. The report reflects a balanced perspective on the views expressed.

5.2 There is scientific consensus that exposure to air pollution is harmful to people’s health, in relation particularly to premature mortality and morbidity, mainly related to respiratory and cardiovascular disease[23][24]. It is also harmful to the environment generally. Since 2015 the profile of anthropogenic air pollution has changed in Scotland, mainly for the better. An updated analysis of trends shows that many of the most important pollutants including fine particulates are now mostly below accepted existing health based limits. However, areas of concern remain, especially excess levels of nitrogen oxides in city centres and pollutants, specifically ammonia, generated by the agricultural sector which have not reduced.

5.3 Evidence continues to accumulate on the range and scale of pressures and impacts linked to airborne pollution, expanding our understanding of how air pollution is harmful to public health and the environment. Findings from outside the UK suggest that harmful impacts can occur at levels below currently used health based limits[24]. More evidence is also available on effective interventions for reducing people’s exposure, especially to road traffic sourced pollution. Consequently, despite recent encouraging trends and reductions in manmade air pollution in Scotland to date, there remains sCoPe for further beneficial reduction.

5.4 A detailed review of the evidence on human health impacts of exposure to air pollution was undertaken by the working group, together with a comparison of the international and Scottish evidence. This can be found in Annex 5a, and in the full report of the working group, which also provides a list of references supporting the group’s conclusions and recommendations[22].

5.5 Factors that correlate closely with air pollution in terms of impacts on people and the environment have also been considered including noise (especially transport generated noise) and airborne greenhouse gas emissions that contribute to global warming and climate change. Increased awareness of these inter-relationships is needed, as is the potential to link co-beneficial mitigating actions. Given the close linkage between outdoor and indoor air pollution and the high proportion of time spent indoors especially by urban dwellers, indoor air quality has been identified as an important related topic.

5.6 Broader related issues that link to improving health and environmental quality generally have also been considered. These include the public health improvement agenda focused on encouraging less sedentary and more active lifestyles and reducing health inequalities; climate change adaptation policy; the planning system and the role of placemaking; environment, agriculture and land use policies; and transport policy. Improving linkages across these topics, to enable better integration of policy development and implementation, is identified as critical to the success of efforts to improve public health and environmental quality.

5.7 As a minimum, there is a continued need to reduce levels of air pollution to meet existing human and ecosystem health based limits. The international evidence suggests that further reductions in air pollutants would be likely to bring additional public health and environmental benefits, with the biggest gains coming from reducing long-term exposure. Due to the relatively lower exposure levels in Scotland already and the different epidemiology of health impacts here, it is difficult to quantify accurately the scale of any such additional potential benefits.

Conclusions on the evidence on air pollution and health

5.8 The international epidemiological evidence convincingly shows that ambient air pollution causes serious damage to both respiratory and cardiovascular health worldwide, with wide-ranging effects including earlier death. There is no agreed level of the key pollutants (fine particulates (PM2.5), O3 and NO2) at which adverse effects can be said with confidence, not to occur. As noted by WHO in 2013, the evidence of effects of both short-term and long-term exposure continues to grow, with the greatest public health effects being associated with long-term exposures. These findings have for many years formed the basis of air pollution control internationally, as endorsed for example by WHO, The UK Committee on Medical Effects of Air Pollutants (COMEAP) in the UK, the EU, US EPA and many other expert groups.

5.9 The evidence relating to long-term impacts associated with particulate pollution is notably strong, especially for PM2.5, for which there is no agreed threshold level at which adverse effects stop occurring for the population as a whole. Reducing ambient PM levels below international health based standards must therefore remain a high priority, alongside efforts to reduce nitrogen oxides and other preventable pollutants.

5.10 There is some uncertainty from international studies about the scale of health effects associated with low pollutant concentrations typical of the average seen in Scotland now. The specifically Scottish literature, while small, has repeatedly demonstrated impacts of pollutants on respiratory illness that are consistent with international evidence. Studies in Scotland differ from the international evidence however, in not showing effects of pollution on cardiovascular (CV) disease outcomes for reasons that are unknown. The extent to which future policy making in Scotland is based on the international evidence and takes account of the specifically Scottish studies, has implications on the advice that can be given on what additional proportionate action is needed to further reduce the harm due to air pollution at current levels (and where trends in key pollutant concentrations may continue downwards in any case).

5.11 There is growing evidence from other countries showing associations of air pollution with other important health conditions including dementia, diabetes, and adverse pregnancy outcomes (low birth weight and prematurity). Collectively this constitutes good evidence that air pollution, even at the low concentrations found in much of Scotland, is linked to excess ill health that should be preventable by reducing pollution further.

5.12 The fundamental message, based on available evidence, is that air pollution is harmful to human health and the wider environment. Although difficult to predict or measure, further reductions in ambient manmade air pollution will be likely to bring additional public health gains, especially in terms of reduced long-term health impacts across a range of preventable adverse health outcomes.

5.13 Reduction in air pollution over recent decades in Scotland will have reduced the health burden associated with exposure. International evidence suggests that further reductions in human sourced air pollution would be likely to benefit public health in Scotland. However, given that key ambient pollutant levels in Scotland are now relatively low in global terms, it is difficult to predict, and may be hard to demonstrate accurately the level of additional health gain that might result from further reductions in air pollution.

5.14 Effective strategies to reduce air pollution include infrastructure support to encourage increased levels of physical activity via more active travel (walking and cycling); encouraging less reliance on private vehicles by improving access to affordable, available public transport; and improving public transport quality and choice to encourage more switching to zero and low emission vehicles. To achieve significant change in aspects of everyday business and domestic life, as well as modal shift in transport use, a better understanding is needed of current public perceptions of air pollution, as well as of motivations and barriers that impede needed changes.

5.15 Achieving these aims in a more coordinated way will also require concerted action to make health focused policy development more of a joint priority across all relevant central and local government departments (e.g. health, environment, transport, agriculture and especially planning, placemaking and development). To achieve meaningful change, all stakeholders (e.g. government, business and industry, employers (private and public) as well as the public themselves) acting as generators of pollutant emissions generally and especially as users of transport, will need to be encouraged to play their part in helping to prevent the future health burden associated with avoidable air pollution.

5.16 Finally, there are both human rights aspects to the effects and impacts of air pollution on health as well as issues around the distribution of costs and benefits here and these require further and fuller recognition and response. Future work should interrogate the existing Scottish Index of Multiple Deprivation (SIMD) data to explore evidence of links between socially deprived communities and air quality. For example, if the main form of transport in these communities is bus then as the move to newer buses within city centres progresses then older buses may be used within peripheral areas, exacerbating disadvantage. Anecdotal evidence in Glasgow and Edinburgh supports this recent trend. Research in 2018[25] from Glasgow University looked at how economic development and urban planning decisions can both increase the links between social deprivation and poor air quality, but can also lead to improvement. Implementation measures to tackle air pollution must avoid embedding environmental injustice into proposed solutions. It is clear from even initial consideration of transport poverty as well as socio-economic conditions generally that we should better understand and address the health inequalities aspects of air pollution. Evidently those who generate the least air pollution may be those who suffer its effects most and vice versa.

5.17 In summary therefore, air pollution causes harm to human health and, while there have been valuable identifiable improvements in some areas, the impacts are serious and require to be addressed, both in order to achieve comprehensive legal compliance with EU and WHO standards and to provide appropriate precautionary protection to the population, not least those sensitive receptors upon whom pollution can have the most acute impacts.

5.18 There is a clear need to ensure all relevant sectors, including all Scottish Government and local government departments and agencies work coherently and effectively together to adopt a joint approach to achieving integrated positive health-focused policies which deliver lower air pollution, better health outcomes and the suite of possible co-benefits for and with the population.

Recommendations – evidence for health impacts

H1. Further consideration of evidence on health impacts of low level pollution in countries with levels of ambient air pollution comparable to Scotland is needed.

H2. Commission population research on the long term effects of air pollution using cohort methods to aid further understanding of health impacts and explain the apparently different epidemiology in Scotland.

Potential co-benefits to public health of reducing air pollution

5.19 Policies that improve air quality can potentially have multiple co-benefits for population health, for addressing inequality and for mitigating and adapting to climate change. A prime example is policy to promote active travel. Walking and cycling increase physical activity and significantly reduce cardiovascular incidence and mortality, and have been shown to reduce all-cause mortality even after controlling for other physical activity[26],[27],[28]. Commuters who transitioned from using a car to active travel or public transport showed reductions in body mass[29]. Substantial potential savings in health care costs have been estimated for increased levels of active travel in urban areas[30]. Evidence shows that the physical activity benefits of active travel outweigh the harm caused by potentially more exposure to air pollution in all but the most extreme situations[31]. However, walking and cycling in places with noticeable poor air quality is a disincentive. Measures to reduce traffic sourced air pollution and to increase levels of active travel can therefore amplify benefits to public health and help to meet sustainability goals. Further detail on the health and cost impacts of interventions reducing traffic sourced air pollution can be found in Annex 5b.

Recommendation – co-benefits

 H3. An Air Pollution Action Plan should be developed and implemented with actions and investment, focussed on joint actions across all relevant government departments, agencies and local government functions to increase levels of active and sustainable travel. This should include integrated and complementary approaches to improve air quality, to reduce carbon emissions and to reduce related health inequalities.

Public Perceptions of Air Pollution

5.20 Creating a policy and physical environment that encourages less polluting, more active and healthier lifestyles is an essential but not sufficient requirement to achieve change. The perceptions and attitudes of key stakeholder groups, especially the public, to both the importance of the issues and the case for change are key factors to be addressed. There is limited research on public attitudes to air pollution as a topic.

5.21 DEFRA published qualitative research involving car users, public transport users and other identified groups, gauging levels of knowledge, public understanding and attitudes to the issues[32], the results of which are summarised in Annex 5c. This survey was restricted to England and Wales and may not be representative of the position in Scotland. Similar research to understand levels of concern and attitudes to air pollution among the general public and key stakeholder groups in Scotland, would therefore be helpful, along with research on barriers and willingness to change pollution generating behaviours (see General Recommendation 4 above).

Co-related aspects of air pollution and health

5.22 The public health effects of indoor air quality, noise pollution and climate change correlate strongly with those of outdoor air pollution; effort to address these issues in a more coordinated way offers additional potential co-benefits. Evidence based action to reduce air pollution has clear potential co-benefits in terms of supporting the aims of a range of government policies aimed at: improving public health and reducing health inequalities; environmental quality improvement, climate change mitigation and adaptation; reducing noise pollution and creating a more sustainable transport system.

Air pollution and noise

5.23 As yet there are no fixed noise level targets in the UK. The EU adopted a Directive on environmental noise in 2002, which stipulates that measurements must be taken of ambient noise; the results must be made publicly available and action plans for noise reduction must be agreed.  WHO published guidance in 2018 on environmental noise levels taking account of existing health effects evidence[33].

5.24 In Scotland’s four major cities alone, it has been estimated that over 1 million people are exposed to noise levels in excess of the WHO guidelines during the daytime and over 0.8 million during the night, with evidence indicating that deprived communities suffer more[34]. The costs of increased health impacts have not been estimated in Scotland directly but based on WHO estimates elsewhere are potentially considerable. Further detail on the impacts of noise exposure for wildlife and humans can be found in Annex 5d.

5.25 The major source of ambient noise is from road traffic, the same source as much ambient air pollution. Studies have identified links between road traffic noise and cardiovascular impacts[35]. The adverse impacts of air pollution are closely correlated with those of noise, making it difficult to assess the impact of traffic noise on health separately. However, this also means that some interventions aimed at reducing traffic sourced air pollution are also likely to help reduce excess traffic sourced noise. These interventions range from traffic reduction in urban areas to physical responsive solutions such as green (living plant) barriers along roads, where evidence suggests these can reduce both traffic-related air pollution and noise[36]. General Recommendation 2 above covers the need for any plan aiming to reduce noise to be aligned with other plans such as air quality action plans and those coving climate change adaptation and mitigation.

Air pollution and climate change

5.26 Scottish carbon emissions have reduced in the last 15 years. However, transport related carbon emissions have increased as a proportion of the Scottish total rising from 32.7% of greenhouse gases in 2015 to 37.3% in 2016 and in real terms, with transport mass emissions increasing by 2.3% between 2015 and 2016. As 68% of total transport emissions in Scotland are related to traffic, greenhouse gas emissions are therefore closely linked to road traffic sourced air pollution[37].

5.27 The CAFS GG commissioned a report from a Climate Change Sub-group to assess the likely co-benefits between climate change and air quality improvement actions[38].

5.28 Of the 50 recommendations made in the report, 38 presented strong evidence of synergies between tackling climate change and improving air quality simultaneously. Only three recommendations revealed some potential for tension.


H4. It is strongly recommended that, at all levels of governance, when actions are being taken to address air quality then they be screened to maximise the potential for co-benefits with climate change mitigation and adaptation. The reverse should also be the case. The screening should, at minimum, be against the 50 recommendations in the CAFS GG Climate Change sub-group Report.

Indoor air quality

5.29 Indoor air quality is determined by multiple factors including ambient outdoor air pollution[39]. Unlike outdoor air quality, there are no regulated limits for indoor pollutants in domestic settings in the UK. The WHO published guidelines in 2010 on safe concentrations of indoor air pollutants for general use and the Health and Safety Health Executive (HSE) publish occupational limits for a range of workplace air pollutants[40].

5.30 Urban populations in the UK spend around 90% of their time indoors; the quality of the indoor air is therefore at least as important as that of outdoor air. Around 50% to 75% of the variability of indoor concentrations of common pollutants (NOx, SO2, O3, and PM) is estimated to be explained by variation in outdoor pollution[41]. This makes estimating the health impacts of indoor air quality alone very challenging.

5.31 New reviews of indoor air pollution and health impacts are currently under way in the UK, including by National Institute for Health and Care Excellence (NICE), but will not report for some time. Further detail on the sources and health effects of indoor air pollution can be found in Annex 5e.

5.32 Although multiple government departments have a role to play, no single Government department (in UK or Scottish Governments) has sole responsibility for indoor air quality. There is therefore a need for policy integration and coherence being pursued to avoid the risks of unintended consequences. This applies generally as shown by the increase in NO2 emissions associated with the switch to diesel engines encouraged by Government to help reduce CO2 emissions and specifically in relation to indoor air quality. Changes determined by non-health related policy drivers (e.g. floor surfaces, cleaning policy, sealed windows and air conditioning or the drive for energy efficiency to reduce global warming gas emissions) could have unexpected adverse health consequences, if these are not viewed in the round, anticipated and mitigation measures identified.

5.33 As well as links to outdoor air pollution, indoor air pollution is therefore a complex issue in its own right with unique determinants. As a topic, it therefore merits more collective attention to assess its significance in relation to public health. A coordinated approach across government departments and other stakeholders is therefore needed to create a focus for a future cross-government indoor air quality strategy.


H5. It is strongly recommended that a task group be convened to identify what, if any, actions might best be undertaken at Scottish level to address the issues associated with indoor air pollution.

In-vehicle air quality

5.34 Throughout this review, from time to time the issue of air pollution inside vehicles has arisen. It has sometimes been seen as a minor issue or one too complex or anecdotal to consider and we have not been able to prioritise it in this report. However, both inside cars and vans as well as onboard buses, especially during warmer weather where windows may be open, for example, and where traffic is static with engines running for extended periods, pollution from other vehicles and sources may enter the cabin and be breathed in by driver and passengers alike. Where public transport is used by already disadvantaged groups and by the elderly, the ill, or pregnant women or parents with young babies and children for example, this could have compounding ill-health effects. Stop-start engines and efficient and effective filtration systems will have fuel consumption and pollution impacts of their own. We also note that general improvements in future to air quality will contribute to reducing pollution inside vehicles. Nonetheless at this point there is little factual basis to conclude whether the problem is serious or not.

5.35 This highlights too the issue of actual individual exposures versus generalised data based upon place of residence, work place or other point data used to look at samples and populations that may not reflect the experience of the individual’s day, life and cumulative exposure generally. We have received anecdotal evidence of some modern cars “cleaning” ambient air as it passes through the filters of the vehicle and comparisons with those smoking in a vehicle and direct and passive impacts on passengers.  At this point, we are able therefore simply to make two recommendations.


H6. Consideration should be given to research on in-vehicle exposures and potential health impacts to provide a factual baseline.[42]

H7. Consideration should be given to a “habit survey” type assessment of actual exposures experienced by a representative sample of the population, assessing pollution exposures over a realistic “normal activity range over a normal period”[43].

These recommendations would allow stronger and more meaningful inference around the significance of real exposures to the average person and thus where further policy developments and potential interventions may need to be made.



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