There are known links between air pollution and more severe mental illness. Previous ARC South London research found small rises in exposure to air pollution led to a higher risk of treatment being required by service users with pre-existing mood and psychotic disorders.
Among people with dementia, increased community mental health team usage is associated with higher levels of residential air pollution. If these links are causal, reducing air pollution would reduce health service use in polluted areas, improving the mental health of residents and reducing healthcare costs.
Measures including low emission zones and congestion charges have been implemented in many large cities, and there is evidence that these measures improve safety and physical health. London has had a low emission zone for vehicles since 2008, succeeded by the T-Charge in 2017 and the ULEZ in 2019.
Since 2019, the ULEZ has been in effect 24 hours per day, every day, for the initial inner-city area. The zone has been expanding and now covers all of London, reducing the number of vehicles on the road and measurably decreasing air pollution.
Preliminary findings show a subsequent impact or cardio-respiratory health. However, there is not currently an evaluation of the ULEZ and its impact on population mental health and mental health service users. We want to know how mental health service use and mortality have been affected by the implementation of ULEZ and subsequent improvements to air quality.
This research will benefit urban-dwelling people of all ages by increasing our understanding of possible benefits for population mental health during and after the ULEZ implementation. The findings will also be used to inform urban planning policies for healthier cities in the future.
The aim of the project is to quantify the impact of the ULEZ on mental health service use, hospital, admissions, and mortality within south London. The research team want to identify potential heath inequities in terms of ethnicity and socio-economic deprivation.
We are aware that service users living in neighbourhoods with high deprivation and the Black Caribbean/African population in south London are exposed to higher levels of air pollution than service users living in affluent neighbourhoods and White ethnic populations. Our project will unpick those associations by looking at ethnicity and neighbourhood deprivation to understand which populations are impacted the most in terms of their mental health, with a view to informing targeted prevention strategies and interventions.
The target population of this research are mental health service users with psychiatric or neurological conditions of any age (including those under 18 years old) living within the boroughs of Lambeth, Southwark, Lewisham, and Croydon at any point from four years before the implementation of the ULEZ until the start of the Covid-19 period.
The researchers will obtain and analyse an observational sample of all South London and Maudsley (SLAM) service users in those boroughs who registered with the service between January 2015 and February 2020.
In the first stage of the research, residents in the ULEZ area will be matched with individuals living in non-ULEZ areas based on age, gender, ethnicity, neighbourhood deprivation, month and year of first contact with secondary mental health services.
In the second stage of the research, the individuals living in the ULEZ area will be compared with those living in non-ULEZ areas, with the researchers looking at changes in mortality, mental health service use and hospital admissions that occurred around the implementation of ULEZ, accounting for seasonal changes and other variables.
The researchers are working with ARC South London’s applied informatics team and NIHR Health Protection Research Unit in Environmental Exposures and Health at Imperial College London.
The project is being designed based on feedback from the NIHR ARC South London PPI (patient and public involvement) group and will involve PPI throughout the project analysis and dissemination.
The project began in November 2023 and is expected to complete in March 2026.
Read more about the economics and biostatistics research at ARC South London.
Read more about the applied informatics research ARC South London.
