• Marshall Lloyd, Toyib Olaniyan, Arman Ganji, Junshi Xu, Alessya Venuta, Leora Simon, Mingqian Zhang, Milad Saeedi, Shoma Yamanouchi, An Wang, Alexandra Schmidt, Hong Chen, Paul Villeneuve, Joshua Apte, Eric Lavigne, Richard T Burnett, Michael Tjepkema, Marianne Hatzopoulou, and Scott Weichenthal.
• McGill University Department of Epidemiology Biostatistics and Occupational Health, Montreal, Quebec, Canada.
• Am. J. Respir. Crit. Care Med. 2024 Jun 26.

RationaleOutdoor fine particulate air pollution (PM2.5) contributes to millions of deaths around the world each year, but much less is known about the long-term health impacts of other particulate air pollutants including ultrafine particles (a.k.a. nanoparticles) which are in the nanometer size range (<100 nm), widespread in urban environments, and not currently regulated.ObjectivesEstimate the associations between long-term exposure to outdoor ultrafine particles and mortality.MethodsOutdoor air pollution levels were linked to the residential addresses of a large, population-based cohort from 2001 - 2016. Associations between long-term exposure to outdoor ultrafine particles and nonaccidental and cause-specific mortality were estimated using Cox proportional hazards models.MeasurementsAn increase in long-term exposure to outdoor ultrafine particles was associated with an increased risk of nonaccidental mortality (Hazard Ratio = 1. 073, 95% Confidence Interval = 1. 061, 1. 085) and cause-specific mortality, the strongest of which was respiratory mortality (Hazard Ratio = 1.174, 95% Confidence Interval = 1.130, 1.220).Main ResultsLong-term exposure to outdoor ultrafine particles was associated with increased risk of mortality. We estimated the mortality burden for outdoor ultrafine particles in Montreal and Toronto, Canada to be approximately 1100 additional nonaccidental deaths every year. Furthermore, we observed possible confounding by particle size which suggests that previous studies may have underestimated or missed important health risks associated with ultrafine particles.ConclusionsAs outdoor ultrafine particles are not currently regulated, there is great potential for future regulatory interventions to improve population health by targeting these common outdoor air pollutants.

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