photo low emissionAir 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.

PI: Dr Sean Beevers