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

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, quasiexperimental 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.