All-cause, cardiovascular, and respiratory mortality and wildfire-related ozone: a multicountry two-stage time series analysis

Background Wildfire activity is an important source of tropospheric ozone (O-3) pollution. However, no study to date has systematically examined the associations of wildfire-related O-3 exposure with mortality globally. Methods We did a multicountry two-stage time series analysis. From the Multi-City Multi-Country (MCC) Collaborative Research Network, data on daily all-cause, cardiovascular, and respiratory deaths were obtained from 749 locations in 43 countries or areas, representing overlapping periods from Jan 1, 2000, to Dec 31, 2016. We estimated the daily concentration of wildfire-related O-3 in study locations using a chemical transport model, and then calibrated and downscaled O-3 estimates to a resolution of 0<middle dot>25 degrees x 0<middle dot>25 degrees (approximately 28 km 2 at the equator). Using a random-effects meta-analysis, we examined the associations of short-term wildfire-related O-3 exposure (lag period of 0-2 days) with daily mortality, first at the location level and then pooled at the country, regional, and global levels. Annual excess mortality fraction in each location attributable to wildfire-related O-3 was calculated with pooled effect estimates and used to obtain excess mortality fractions at country, regional, and global levels. Findings Between 2000 and 2016, the highest maximum daily wildfire-related O-3 concentrations (>= 30 mu g/m (3) ) were observed in locations in South America, central America, and southeastern Asia, and the country of South Africa. Across all locations, an increase of 1 mu g/m (3) in the mean daily concentration of wildfire-related O-3 during lag 0-2 days was associated with increases of 0<middle dot>55% (95% CI 0<middle dot>29 to 0<middle dot>80) in daily all-cause mortality, 0<middle dot>44% (-0<middle dot>10 to 0<middle dot>99) in daily cardiovascular mortality, and 0<middle dot>82% (0<middle dot>18 to 1<middle dot>47) in daily respiratory mortality. The associations of daily mortality rates with wildfire-related O-3 exposure showed substantial geographical heterogeneity at the country and regional levels. Across all locations, estimated annual excess mortality fractions of 0<middle dot>58% (95% CI 0<middle dot>31 to 0<middle dot>85; 31 606 deaths [95% CI 17 038 to 46 027]) for all-cause mortality, 0<middle dot>41% (-0<middle dot>10 to 0<middle dot>91; 5249 [-1244 to 11 620]) for cardiovascular mortality, and 0<middle dot>86% (0<middle dot>18 to 1<middle dot>51; 4657 [999 to 8206]) for respiratory mortality were attributable to short-term exposure to wildfire-related O-3 . Interpretation In this study, we observed an increase in all-cause and respiratory mortality associated with short-term wildfire-related O-3 exposure. Effective risk and smoke management strategies should be implemented to protect the public from the impacts of wildfires. Copyright (c) 2024 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license.