Mortality attributable to ambient fine particulate matter and nitrogen dioxide in Switzerland in 2019: Use of two-pollutant effect estimates.

Air pollution health risk assessments have traditionally used single-pollutant effect estimates for one proxy ambient air pollutant such as PM 2.5. Two-pollutant effect estimates, i.e. adjusted for another correlated pollutant, theoretically enable the aggregation of pollutant-specific health effects minimizing double-counting. Our study aimed at estimating the adult mortality in Switzerland in 2019 attributable to PM 2.5 from a single-pollutant effect estimate and to the sum of PM 2.5 and NO 2 from two-pollutant estimates; comparing the results with those from alternative global, European and Swiss effect estimates. For the single-pollutant approach, we used a PM 2.5 summary estimate of European cohorts from the project ELAPSE, recommended by the European Respiratory Society and International Society for Environmental Epidemiology (ERS-ISEE). To derive the two-pollutant effect estimates, we applied ELAPSE-based conversion factors to ERS-ISEE PM 2.5 and NO 2 single-pollutant effect estimates. Additionally, we used World Health Organization 2021 Air Quality Guidelines as counterfactual scenario, exposure model data from 2019 and Swiss lifetables. The single-pollutant effect estimate for PM 2.5 (1.118 [1.060; 1.179] per 10 μg/m3) resulted in 2240 deaths (21,593 years of life lost). Using our derived two-pollutant effect estimates (1.023 [1.012; 1.035] per 10 μg/m3 PM 2.5 adjusted for NO 2 and 1.040 [1.023; 1.058] per 10 μg/m3 NO 2 adjusted for PM 2.5), we found 1977 deaths (19,071 years of life lost) attributable to PM 2.5 and NO 2 together (23% from PM 2.5). Deaths using alternative effect estimates ranged from 1042 to 5059. Estimated premature mortality attributable to PM 2.5 alone was higher than to both PM 2.5 and NO 2 combined. Furthermore, the proportion of deaths from PM 2.5 was lower than from NO 2 in the two-pollutant approach. These seemingly paradoxical results, also found in some alternative estimates, are due to statistical imprecisions of underlying correction methods. Therefore, using two-pollutant effect estimates can lead to interpretation challenges in terms of causality. [Display omitted] • We used single- and two-pollutant effect estimates from ELAPSE cohorts in Europe. • The single-pollutant estimates for PM 2.5 yielded 2240 deaths. • The two-pollutant estimates for PM 2.5 and NO 2 summed 1977 deaths (23% from PM 2.5). • The results were within the range of those using alternative effect estimates. • Two-pollutant estimates led to paradoxical results and interpretation challenges. [ABSTRACT FROM AUTHOR]