Association between Mortality and Short-Term Exposure to Particles, Ozone and Nitrogen Dioxide in Stockholm, Sweden

Abstract

In this study, the effects on daily mortality in Stockholm associated with short-term exposure to ultrafine particles (measured as number of particles with a diameter larger than 4 nm, PNC₄), black carbon (BC) and coarse particles (PM_2.5⁻10) have been compared with the effects from more common traffic-pollution indicators (PM₁₀, PM_2.5 and NO₂) and O₃ during the period 2000⁻2016. Air pollution exposure was estimated from measurements at a 20 m high building in central Stockholm. The associations between daily mortality lagged up to two days (lag 02) and the different air pollutants were modelled by using Poisson regression. The pollutants with the strongest indications of an independent effect on daily mortality were O₃, PM_2.5⁻10 and PM₁₀. In the single-pollutant model, an interquartile range (IQR) increase in O₃ was associated with an increase in daily mortality of 2.0% (95% CI: 1.1⁻3.0) for lag 01 and 1.9% (95% CI: 1.0⁻2.9) for lag 02. An IQR increase in PM_2.5⁻10 was associated with an increase in daily mortality of 0.8% (95% CI: 0.1⁻1.5) for lag 01 and 1.1% (95% CI: 0.4⁻1.8) for lag 02. PM₁₀ was associated with a significant increase only at lag 02, with 0.8% (95% CI: 0.08⁻1.4) increase in daily mortality associated with an IQR increase in the concentration. NO₂ exhibits negative associations with mortality. The significant excess risk associated with O₃ remained significant in two-pollutant models after adjustments for PM_2.5⁻10, BC and NO₂. The significant excess risk associated with PM_2.5⁻10 remained significant in a two-pollutant model after adjustment for NO₂. The significantly negative associations for NO₂ remained significant in two-pollutant models after adjustments for PM_2.5⁻10, O₃ and BC. A potential reason for these findings, where statistically significant excess risks were found for O₃, PM_2.5⁻10 and PM₁₀, but not for NO₂, PM_2.5, PNC₄ and BC, is behavioral factors that lead to misclassification in the exposure. The concentrations of O₃ and PM_2.5⁻10 are in general highest during sunny and dry days during the spring, when exposure to outdoor air tend to increase, while the opposite applies to NO₂, PNC₄ and BC, with the highest concentrations during the short winter days with cold weather, when people are less exposed to outdoor air.

Keywords: PM2.5–10; excess risk; exposure; linear regression; mortality; ozone; particle number count (PNC).