Advancing Long-Term Outdoor Air Pollution Exposure Assessment for Health Studies: Lessons from a Multinational Research Initiative.

PURPOSE OF REVIEW: The Health Effects Institute recently completed an extensive research initiative to investigate novel approaches to improve assessment of long-term exposure to outdoor air pollution for health studies in North America and Europe. This overview synthesizes the key results, strengths, and limitations, along with other key research and future research needs. RECENT FINDINGS: Exposures predicted from the various models, including those accounting for daily mobility patterns and outdoor-indoor infiltration rates, generally resulted in moderately to highly correlated exposure estimates (correlation > 0.7). Health effect estimates associated with the alternative exposures were similar, albeit with some notable differences in the magnitude - but not the direction - of the associations. This research initiative can inform decisions about estimating air pollution exposure in epidemiological studies, as investigators balance concerns about bias, efficiency, and resource needs. Future work is needed to replicate findings in other studies and regions. Other areas of future work include generating representative validation data for long-term exposure estimates, propagating exposure measurement error more fully into health effect estimates and improving understanding of the influence of indoor environments.