Emerging evidence has found a link between air pollution and mental disorders. However, more high-quality research is necessary to confirm this association. Adolescence is a critical time of brain development and the age of mental disorder diagnosis. Subsequently, early intervention during this time could prevent the often-lifelong course of mental disorders. The World Health Organisation (WHO) has highlighted air pollution as the most serious threat to human health despite air pollution levels being modifiable. Therefore, the overall aim of this project is to investigate the impact of air pollutants on mental disorders in young people living in Wales between 2000- 2020. This will be achieved using mixed methods e.g., rapid review, data linkage, statistical analysis, and public involvement. Initially, a rapid review will be conducted to assess the research in this area and identify any knowledge gaps. The Secure Anonymised Information Linkage (SAIL) Databank will be used to create a longitudinal cohort by linking individual health, sociodemographic and survey data. The cohort will be linked to air pollution exposure at residence and school location. Additionally, the potential relationships between air pollution and mental disorders will be explored, whilst considering factors such as deprivation. Public involvement will assist the project methodology, direction, dissemination and provide an understanding of individual experiences of mental health in relation to the environment. Therefore, increasing the current knowledge of the effects of air pollution on mental health. The resulting peer review publications could further encourage additional dissemination into public health sector. Thus, encouraging policies to improve air quality. Subsequently, reducing air pollution could help improve holistic health at a population-scale.