Comparison of air pollution mortality effect estimates using different long-term exposure assessment modelling methods

Introduction

Epidemiological studies have used different approaches to assess long-term exposure to ambient air pollution. Little is known about how different exposure models affect health effect estimates in these studies. The aim of this study was to compare air pollution mortality effect estimates in an administrative cohort in the Netherlands based on different exposure assessment methods for black carbon (BC), nitrogen dioxide (NO₂), ultrafine particles (UFP), and particulate matter <2.5 μm (PM_2.5).

Methods

Annual average air pollution exposure estimates using eight methods, differing in modelling and monitoring strategy, were applied to a Dutch national cohort of 10.7 million adults aged ≥30 years. Dispersion and land-use regression models based on mobile and fixed-site monitoring were evaluated. Follow-up was from 2013 to 2019. Hazard ratios (HR) for natural and cause-specific mortality were estimated using Cox proportional hazards models.

Results

Exposure estimates from different models were highly correlated. Even though the direction of mortality effect estimates was similar between methods, their magnitude differed substantially, e.g. the HR for BC with natural mortality ranged from 1.01 to 1.09 per increment of 1 μg/m³. No consistent differences in effect estimates were found between deterministic and empirical fixed-site and mobile models. Model predictions over a 10-year period correlated highly and resulted in similar HRs.

Discussion

Different exposure models resulted in similar conclusions about the presence of associations with mortality, but HRs differed up to a ratio of 1.27. Differences in exposure assessment may therefore contribute to the observed heterogeneity of mortality estimates in systematic reviews of epidemiological studies.