Mortality risk attributable to wildfire-related PM25 pollution: a global time series study in 749 locations

Abstract

Background: Many regions of the world are now facing more frequent and unprecedentedly large wildfires. However, the association between wildfire-related PM25 and mortality has not been well characterised. We aimed to comprehensively assess the association between short-term exposure to wildfire-related PM25 and mortality across various regions of the world.

Methods: For this time series study, data on daily counts of deaths for all causes, cardiovascular causes, and respiratory causes were collected from 749 cities in 43 countries and regions during 2000-16. Daily concentrations of wildfire-related PM25 were estimated using the three-dimensional chemical transport model GEOS-Chem at a 025 025 resolution. The association between wildfire-related PM25 exposure and mortality was examined using a quasi-Poisson time series model in each city considering both the current-day and lag effects, and the effect estimates were then pooled using a random-effects meta-analysis. Based on these pooled effect estimates, the population attributable fraction and relative risk (RR) of annual mortality due to acute wildfire-related PM25 exposure was calculated.

Findings: 656 million all-cause deaths, 151 million cardiovascular deaths, and 68 million respiratory deaths were included in our analyses. The pooled RRs of mortality associated with each 10 gm3 increase in the 3-day moving average (lag 0-2 days) of wildfire-related PM25 exposure were 1019 (95 CI 1016-1022) for all-cause mortality, 1017 (1012-1021) for cardiovascular mortality, and 1019 (1013-1025) for respiratory mortality. Overall, 062 (95 CI 048-075) of all-cause deaths, 055 (043-067) of cardiovascular deaths, and 064 (050-078) of respiratory deaths were annually attributable to the acute impacts of wildfire-related PM25 exposure during the study period.

Interpretation: Short-term exposure to wildfire-related PM25 was associated with increased risk of mortality. Urgent action is needed to reduce health risks from the increasing wildfires.