Analysis of Temporal Variability in the Short-term Effects of Ambient Air Pollutants on Nonaccidental Mortality in Rome, Italy (1998–2014)

OBJECTIVES: The association between short-term air pollution exposure and daily mortality has been widely investigated, but little is known about the temporal variability of the effect estimates. We examined the temporal relationship between exposure to particulate matter (PM) ([Formula: see text] , [Formula: see text]) and gases ([Formula: see text] , [Formula: see text] , and CO) with mortality in a large metropolitan area over the last 17 y. METHODS: Our analysis included 359,447 nonaccidental deaths among [Formula: see text]-old individuals in Rome, Italy, over the study period 1998–2014. We related daily concentrations to mortality counts with a time-series Poisson regression analysis adjusted for long-term trends, meteorology, and population dynamics. RESULTS: Annual average concentrations decreased over the study period for all pollutants (e.g., from [Formula: see text] for [Formula: see text]). Each pollutant was positively associated with mortality, with estimated percentage increases over the entire study period ranging from 0.19% (95% CI: 0.13, 0.26) for a [Formula: see text] increase in CO (0–1 d lag) to 3.03% (95% CI: 2.44, 3.63) for a [Formula: see text] increase in [Formula: see text] (0–5 d lag). We did not observe clear temporal patterns in year- or period-specific effect estimates for any pollutant. For example, we estimated that a [Formula: see text] increase in [Formula: see text] was associated with 1.16% (95% CI: 0.53, 1.79), 0.99% (95% CI: 0.23, 1.77), and 1.87% (95% CI: 1.00, 2.74) increases in mortality for the periods 2001–2005, 2006–2010, and 2011–2014, respectively, and corresponding estimates for a [Formula: see text] increase in [Formula: see text] were 4.20% (95% CI: 3.15, 5.25), 1.78% (95% CI: 0.73, 2.85), and 3.32% (95% CI: 2.03, 4.63). CONCLUSIONS: Mean concentrations of air pollutants have decreased over the last two decades in Rome, but effect estimates for a fixed increment in each exposure were generally consistent. These findings suggest that there has been little or no change in the overall toxicity of the air pollution mixture over time. https://doi.org/10.1289/EHP19