Date of Award

January 2026

Document Type

Open Access Thesis

Degree Name

Master of Public Health (MPH)

Department

School of Public Health

First Advisor

Zeyan Liew

Abstract

Background: Black carbon (BC) is a particulate matter component that is closely linked to combustion and traffic sources, serving as both a short-lived climate pollutant and a potential risk factor for brain health. Despite a substantial burden of adult mental health disorders and cognitive decline, epidemiological evidence on BC exposure and brain health remains scattered.Objective: To systematically map study types, main findings, evidence gaps, and methodological limitations regarding BC exposure and its proxy indicators, such as PM₂.₅ absorbance and elemental carbon in relation to mental health and cognitive outcomes in adults. Methods: Following PRISMA-ScR guidelines, I searched PubMed, Web of Science, and Scopus through December 2025. Eligible studies were observational, conducted among adults (≥18 years), and examined BC or proxy indicators in relation to mental health or cognitive outcomes. Study design, population, exposure assessment, outcomes, and effect estimates were extracted. Results: Sixteen studies met inclusion criteria, conducted across China (5), the United States (5), France (2), and Europe (4). 14 of 16 studies (87.5%) reported statistically significant positive associations between BC exposure and adverse mental health or cognitive outcomes. Effect estimates for depression ranged from OR≈1.12–1.13 to HR=1.03, while cognitive outcomes included a 4.5% decline in processing speed per IQR BC increase and HR=1.10 for incident dementia. Two studies reported null or heterogeneous findings, both in lower-pollution settings. Conclusion: Accumulating epidemiological evidence indicates BC exposure has adverse neurological outcomes across diverse populations and study designs. However, heterogeneity in exposure assessment, co-pollutant confounding, and residual confounding limit causal inference. Future research would focus on longer follow-up designs that incorporate residential mobility to better isolate BC effects from correlated urban exposures.

Comments

This is an Open Access Thesis.

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