Temporal Variation in the Association Between Short-term Exposure to Fine Particulate Matter and Mortality Across...

Growing evidence suggests that the health impacts of a given increment of fine particulate matter (PM 2.5 ) are changing over time. While these trends could influence environmental health disparities, how temporal trends vary across locations and subpopulations remains unknown. Using case-crossover analyses, we analyzed how PM 2.5 -mortality associations varied over time (2001-2016) in two U.S. states (North Carolina and Michigan) among persons 65+ years of age. We further characterized temporal variation in the PM 2.5 -mortality association by sociodemographic variables including age, sex, race/ethnicity, educational attainment, urbanicity, and substate region. From the 2001-2008 study period to the 2009-2016 study period, the odds of mortality per 10 μg/m 3 PM 2.5 decreased by 0.77% in North Carolina but increased by 0.28% in Michigan. Using a nonlinear temporal model, the associations between PM 2.5 concentration and mortality were variable over time in North Carolina and steadily increased over time in Michigan. We also found suggestive evidence of widening disparities in PM 2.5 -mortality odds ratios over time. For example, PM 2.5 -mortality odds in Michigan increased more dramatically for non-Hispanic black (1.71% [-1.17, 4.67%]) than for non-Hispanic white (0.14% [95% confidence interval (CI) = -0.93, 1.22%]) subpopulations. In North Carolina, these groups experienced a 0.40% (-3.56, 2.85%) and 0.96% (-2.52, 0.62%) reduction in PM 2.5 -mortality, respectively. Our results suggest that PM 2.5 -related mortality impacts may be changing over time, with different trends by location and subpopulation, potentially exacerbating environmental injustice.