Exposure to PM2.5 air pollution and mortality in Northern Ireland

Objective and ApproachThis study assesses the relationship between PM2.5 air pollution exposure and mortality in Northern Ireland. It draws on a rich array of individual-level mortality and Census data from the Northern Ireland Longitudinal Study linked to finely grained neighbourhood-level modelled air pollution data. ResultsCox proportional hazards models reveal associations between mortality risk and PM2.5 exposure, though the magnitude of the effects depends on the specification. Without adjustment for measured characteristics, an interquartile range increase in the five-year moving average of PM2.5 exposure is associated with a relatively large increase in the hazard of mortality. This effect is reduced after adjusting for individual-level demographic, socioeconomic and health-related factors as well as household-level factors; however, the hazard ratio remains above one and comparable with estimates from other studies. In further analysis focusing on changes in exposure resulting from address changes, propensity score matching is used to assess whether, among those with similar levels of pre-move exposure, those who move to areas with different pollution levels face subsequently different mortality risks. The results show a higher (lower) mortality risk for those moving to a higher (lower) pollution neighbourhood. Conclusions and ImplicationsThis study provides evidence of mortality effects of PM2.5 from a setting in which annual mean PM2.5 concentrations are low by international standards (averaging roughly 8 micrograms per cubic metre during the study period) and offers timely evidence to inform the delivery of Northern Ireland’s first-ever Clean Air Strategy.