Public Health Impacts of UK's Clean Air Zones.

Air pollution is the greatest environmental threat to health in the UK. Each year it contributes to 30,000 deaths in people under the age of 75 and costs our economy £20 billion. The UK government has committed to reduce the amount of particulate matter (PM), a harmful component of air pollution, in the air we breathe to meet the World Health Organisation's guidance. Clean Air Zones (CAZ), areas where targeted action is taken to improve air quality, are increasingly planned across the world. However, we do not know what effect these CAZs have on air pollution levels or health.
In April 2019 London was the first UK city to implement a large-scale CAZ, the Ultra Low Emission Zone (ULEZ) which covers an area of central London with 200,000 residents. From 2021 it will cover a larger area inside the North and South circular roads that is home to 3.8 million people.
This programme of research will find out if the ULEZ changes air quality and what impact it has on the health of London's residents. We will then repeat the study looking at the planned CAZ in Birmingham to learn more about how CAZs work in different settings. This information is needed by policy makers and public health practitioners to design effective interventions that improve both air quality and population health.
We will undertake a natural-experiment study of the ULEZ to determine its impact on air quality, pollutant composition, non-communicable disease and health inequalities throughout life.
To do this we will complete four complementary research studies. The first study will describe the change to the amount of pollutants in the air as the ULEZ is introduced (2016-2024). We will use measurements from London's Air Quality Network of monitoring sites to estimate air quality across the whole of London using a model we have developed called the CMAQ-urban model. We will also use innovative methods to look beyond the commonly considered pollutants to include traffic related metals and polycyclic aromatic hydrocarbons.
The second study will explore whether there is any change in the health of London residents as the ULEZ is introduced. We will use an interrupted time series approach to compare the occurrence of health outcomes before (2016-2019) the implementation of the ULEZ to after (2019-2022). Specifically, looking at the number of hospital admissions and primary care consultations for respiratory and cardiovascular diseases, babies' birth weights and whether they were born early, and the number of people who die. We will also explore whether the ULEZ disproportionally affects people's health based on their age, sex, ethnicity, socio-economic status or pre-existing chronic diseases (multi-morbidity). We will then use a point process regression model to link the health information to our air quality models to describe how the concentration of pollutants is related to health.
The third study will predict the impact of the planned CAZ in Birmingham on air quality and health using the findings from the study in London. We will then study the real-world impact of Birmingham's CAZ using the same methods applied to the ULEZ and compare these results with those we predicted.
Finally, we will bring together our findings from London and Birmingham with those from a study of how air pollution affects children's respiratory health, physical activity and obesity (CHILL study) to develop a deeper understanding of how CAZs have an impact on health. Specifically, we will refine a logic model to describe the pathways from CAZs to health and we will apply the Health Effects Institute's Outcomes Evaluation Cycle framework to synthesise policy implications for the UK, Europe and global cities, focused on health inequalities and multi-morbidity.
This programme of research will provide the evidence that is needed to design effective public health interventions that improve air quality and the health and wellbeing of urban residents.

The London Ultra Low Emission Zone (ULEZ) was implemented in April 2019 and will be expanded in 2021. It is a large-scale Clear Air Zone (CAZ) intervention targeting urban air pollution, principally from traffic emissions. CAZs are planned across the UK and global urban jurisdictions. There is a paucity of evidence on the impact of air quality interventions which is hampering international policy decisions. We will undertake a natural-experiment study of ULEZ to determine its impact on 1) air quality, 2) pollutant composition, 3) non-communicable disease (birth outcomes, cardiovascular and respiratory disease), 4) health inequalities and 5) multi-morbidity across the life-course.
Environmental exposure data pre- and post the introduction of the ULEZ will be combined with high temporal and geographical resolution modelling approaches to quantify the impact of ULEZ on London air quality with a focus on composition. We will extend current exposure estimates from the CMAQ-urban model to include traffic related metals and PAHs. We will apply interrupted time-series analysis using a Bayesian hierarchical framework to existing (hospital and birth) and emerging (primary care) healthcare data linked to fine spatial resolution air quality, environmental and demographic data to estimate the impact of ULEZ on exposure and health. We will extend with spatio-temporal point process regression models to estimate exposure-response of modelled air quality over the implementation period (2016-2024). We will test and validate these estimates using real-world data from the planned CAZ in Birmingham.
We will refine our logic model of pathways from CAZ to health by linking this research to the mechanistic findings from a prospective cohort of children (CHILL study). Policy implications for the UK, Europe and global cities, focused on health inequalities and multi-morbidity, will be synthesised through the application of a Health Effects Institute Outcomes Evaluation Cycle framework.

Air pollution is the greatest environmental threat to health in the UK. Our early public engagement found that air pollution is the environmental hazard of most concern to the public. The UK government has committed to reduce the amount of particulate matter (PM), a harmful component of air pollution, to meet the World Health Organisation's guidance on the limits to the amount of PM2.5 in the air we breathe. A key intervention to improve our air quality are Clean Air Zones (CAZ). London is the first UK city to implement a large-scale CAZ, the London Ultra Low Emission Zone (ULEZ).
The central aim of our research is to provide the evidence that is needed to design impactful, effective and cost-effective Public Health intervention and policy that will improve air quality and population health. When implemented, policy will deliver long-term impact by improving the health and wellbeing of urban residents and commuters. We will achieve an impact on policy through our expert advisory roles on influential governmental and non-governmental bodies, including the UK Committee on Medical Effects of Air Pollutants (COMEAP).
This programme of research will advance scientific knowledge on the impact of ULEZ on air quality and health. Knowledge will be generated across multiple disciplines, including public health, environmental exposure assessment, and biostatistics. We will deliver academic impact from this knowledge through the generation and dissemination of novel methodologies, datasets, and research outputs within and across disciplines, nationally and internationally. The knowledge and methods we will generate will be applicable to other settings and contribute to international efforts to assess the impact of other CAZ on health.
We will raise awareness in the wider public about the impact of air pollution on health, including the range of diseases that are caused or worsened by ambient levels of air pollution. We will achieve this by embedding a robust programme of public involvement and engagement throughout the research lifecycle. We will develop our communication strategies and activities with the public to ensure that we provide people with the information they want to support healthier choices and improve their health and wellbeing. We will support public participants to become informed citizens by offering a wealth of skills training and support that are relevant for other civil society activities that benefit the wider public. Successful public involvement will also shape the research programme to strengthen the quality and relevance of our research and further raise its impact.
We will contribute to the skilled workforce by training early career researchers and academics funded through this grant and offer opportunities for established researchers to develop advanced skills. This will focus on the core skills needed for a successful career in academia, policy or public health.
Our strategies for realising the ambitious impacts outlined in this section are detailed in our Pathways to Impact statement.