Critical Gaps in Air Pollution and Health Research: A Systematic Review and an Agenda of Policy-Relevant Science

Abstract

Air pollution is a leading environmental health issue, which is a major and adjustable factor in the morbidity and mortality of diseases in the world. Although the evidence base supporting the correlation between exposure to airborne contaminants (in particular, particulate matter (PM2.5), nitrogen oxides, and ozone) and the development of adverse cardiopulmonary outcomes is sound and well-grounded, it remains constrained by critical epistemological and methodological restrictions. These limitations make it difficult to make strong causal attributions, reduce the fully content of risk in a variety of global settings, and eventually hinder the application of scientific consensus to create a good, fair policy. The article is a critical, synthetic review of enduring and pathological gaps in the air pollution and health literature based on authoritative reviews and seminal studies published in the leading publications. These seven areas of uncertainty can be named and interrogated: The health impact of persistent, low-level exposure to levels below the current regulatory limits; Deep geographical disparities in evidence where insufficiency of data is in the high-burden and low-resource areas; The recalcitrant problem of testing complex and real-life mixture of pollutants; Scattered understanding of the mechanism of action between exposure and systemic disease; Insufficiency of characterization of vulnerability through vulnerable stages and vulnerable populations; A deficit of strict empirical tests on the health effectiveness of policy interventions. It is hoped that by systematically defining these boundaries of uncertainty, a strategic redirection of the scientific inquiry can be triggered by this review. We contend that to fill these gaps, a radical change to longitudinal studies of life-course, quasi-experimental and mixture based analytic designs, translational mechanistic studies, and equity-focused, policy-responsive study designs is required. Sealing such knowledge gaps is not a scholarly endeavor but an immediate requirement of enhancing risk evaluation, enhancing regulatory norms, and reducing the growing health burden in the world due to air pollution in the face of simultaneous climatic and demographic changes.

Introduction

The text provides a comprehensive critical review of air pollution as a major global public health crisis, emphasizing its role as a leading cause of morbidity and mortality worldwide. Air pollution—particularly exposure to pollutants such as PM2.5, NO?, SO?, O?, and volatile organic compounds—is strongly linked to cardiovascular disease, chronic respiratory illness, stroke, lung cancer, and an expanding range of non-respiratory outcomes including metabolic, neurological, and developmental disorders. Despite decades of robust epidemiological, toxicological, and clinical evidence, air pollution remains poorly managed, especially in low- and middle-income countries where exposure levels are highest.

The review highlights persistent knowledge gaps that limit effective risk assessment and policy translation. These include inadequate understanding of chronic low-dose exposure effects, geographic imbalances in evidence (with underrepresentation of high-burden regions), methodological limitations of observational studies for causal inference, and overreliance on single-pollutant models that fail to reflect real-world multipollutant exposures. Additional gaps exist in identifying susceptible subpopulations, linking molecular mechanisms to population-level health outcomes, and empirically evaluating the real health benefits of air quality policies.

Methodologically, the field benefits from interdisciplinary triangulation across epidemiology, experimental studies, and toxicology, but each approach has limitations that contribute to uncertainty in exposure–response relationships, particularly at low pollution levels. The review argues that these uncertainties hinder equitable and effective regulation.

To address these challenges, the paper proposes future research priorities, including life-course longitudinal studies, region-specific research in high-burden areas, expanded use of quasi-experimental and causal inference methods, adoption of exposomic and multipollutant frameworks, and stronger integration of mechanistic and epidemiological research. It also stresses the need for equity-centered science that formally models vulnerability and environmental injustice, along with accountability research to rigorously evaluate the health impacts of air quality and climate policies.

Overall, the study calls for a paradigm shift toward interdisciplinary, translational, and policy-relevant research to close critical gaps, strengthen causal understanding, and support effective, equitable interventions against the global health burden of air pollution.

Conclusion

Air pollution remains as a powerful, but solvable, contributor to disease burden and mortality in the world. Rather, as this analysis shows, this scientific consensus translation into decisive, equitable, and maximum effective public health policy is blocked by the systematic and strategic gaps in the evidence base. Although the relationship between exposure and harm cannot be disputed, there are still critical doubts about the extent of risk of chronic low-level exposure, the toxicity of pollutant mixtures, the entire pathophysiological picture, and the selective vulnerability of populations and geographies. The current synthesis reveals a factual mismatch between the most well-answered questions according to the available research and the most urgent ones when it comes to policy making. The practice of long-standing dependence on short-term, single-pollutant, and observationally constrained research, combined with a highly inequitable geographic dissemination of proof, creates danger assessments of an inadequately high level of accuracy and generalizability. As a result, regulatory standards, commonly set by reference to data on healthier populations in high-income locations, cannot be used to safeguard those most at risk: communities with complex exposures, greater baseline exposures, and overlapping socioeconomic risks. These gaps in science directly create policy gaps. Without the definitive life-course studies the long-term economic advantages in terms of pollution control are underestimated. The absence of strong evidence as in the high-burden regions does not give the local policymakers contextual information that can be used effectively in lobbying against other development priorities. In a location where mechanistic pathways are not well defined, standards cannot be optimally directed to the most toxic sources of emissions. Most importantly, the lack of serious policy evaluation studies kills the feedback loop, which is necessary to improve the process of improvement over and over again, so the effectiveness of billion-dollar interventions is only assumed and not conceptually supported. Thus, the direction of future research should be strategically and fundamentally redesigned to support the interests of the population health. The highest rating should be given to longitudinal life-course cohorts that can measure cumulative risk; quasi-experimental studies can mean that offer a causal study of intervention effectiveness; mixture-based exposomic models reflecting the complexity of the real world; and equity focused approaches that explicitly diagnose and remedy environmental injustice. And this is not only an academic agenda, but a state of evidence-based governance. Finally, because of the co-occurring climatic change, population movement to urban areas and demographics, air pollution is a dynamic issue, rather than a static one. The knowledge gaps between these populations need to be bridged urgently to prevent active threats on population health. It requires long-term funding of interdisciplinary science and decolonized research capacity, and the commitment of an iron fist to the view that scientific inquiry, at every stage and throughout its creation, is oriented so as to cast light on the way to actionable, equitable, and health protecting policy.

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Copyright

Copyright © 2026 Saalah Yakubu Saalah, Umar Jiddum Jidda, Abba Jato Ibrahim, Ishaq Iliyas Ishaq, Aliyu Hassan Muhammad, Ali Muhammad Kole, Ibrahim Umar Asheikh. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.