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. 2023 Oct 4:383:e075203.
doi: 10.1136/bmj-2023-075203.

Interactive effects of ambient fine particulate matter and ozone on daily mortality in 372 cities: two stage time series analysis

Cong Liu  1 , Renjie Chen  1 , Francesco Sera  2 , Ana Maria Vicedo-Cabrera  3   4 , Yuming Guo  5   6 , Shilu Tong  7   8   9   10 , Eric Lavigne  11   12 , Patricia Matus Correa  13 , Nicolás Valdés Ortega  13 , Souzana Achilleos  14 , Dominic Roye  15   16 , Jouni Jk Jaakkola  17   18 , Niilo Ryti  17   18 , Mathilde Pascal  19 , Alexandra Schneider  20 , Susanne Breitner  20   21 , Alireza Entezari  6   22 , Fatemeh Mayvaneh  22 , Raanan Raz  23 , Yasushi Honda  24 , Masahiro Hashizume  25 , Chris Fook Sheng Ng  26 , Vânia Gaio  27   28 , Joana Madureira  27   29   30 , Iulian-Horia Holobaca  31 , Aurelio Tobias  26   32 , Carmen Íñiguez  16   33 , Yue Leon Guo  34   35   36 , Shih-Chun Pan  35 , Pierre Masselot  37   38 , Michelle L Bell  39 , Antonella Zanobetti  40 , Joel Schwartz  40 , Antonio Gasparrini  37   38   41 , Haidong Kan  42   43
Affiliations

Interactive effects of ambient fine particulate matter and ozone on daily mortality in 372 cities: two stage time series analysis

Cong Liu et al. BMJ. .

Abstract

Objective: To investigate potential interactive effects of fine particulate matter (PM2.5) and ozone (O3) on daily mortality at global level.

Design: Two stage time series analysis.

Setting: 372 cities across 19 countries and regions.

Population: Daily counts of deaths from all causes, cardiovascular disease, and respiratory disease.

Main outcome measure: Daily mortality data during 1994-2020. Stratified analyses by co-pollutant exposures and synergy index (>1 denotes the combined effect of pollutants is greater than individual effects) were applied to explore the interaction between PM2.5 and O3 in association with mortality.

Results: During the study period across the 372 cities, 19.3 million deaths were attributable to all causes, 5.3 million to cardiovascular disease, and 1.9 million to respiratory disease. The risk of total mortality for a 10 μg/m3 increment in PM2.5 (lag 0-1 days) ranged from 0.47% (95% confidence interval 0.26% to 0.67%) to 1.25% (1.02% to 1.48%) from the lowest to highest fourths of O3 concentration; and for a 10 μg/m3 increase in O3 ranged from 0.04% (-0.09% to 0.16%) to 0.29% (0.18% to 0.39%) from the lowest to highest fourths of PM2.5 concentration, with significant differences between strata (P for interaction <0.001). A significant synergistic interaction was also identified between PM2.5 and O3 for total mortality, with a synergy index of 1.93 (95% confidence interval 1.47 to 3.34). Subgroup analyses showed that interactions between PM2.5 and O3 on all three mortality endpoints were more prominent in high latitude regions and during cold seasons.

Conclusion: The findings of this study suggest a synergistic effect of PM2.5 and O3 on total, cardiovascular, and respiratory mortality, indicating the benefit of coordinated control strategies for both pollutants.

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Conflict of interest statement

Competing interests: All authors have completed the ICMJE uniform disclosure form at URL www.icmje.org/disclosure-of-interest/ and declare: support from the National Natural Science Foundation of China and the Italian Ministry of University and Research; no financial relationships with any organizations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

Figures

Fig 1
Fig 1
Percentage changes (central estimates and 95% confidence interval) in total, cardiovascular, and respiratory mortality associated with a 10 μg/m3 increase in PM2.5 and O3 in stratified analyses and in high and low latitude regions. High latitude (n=186), latitude above median (absolute value of 40.3°) across all cities; low latitude (n=186), latitude below median across all cities. P values for interactions were obtained from likelihood ratio tests. CI=confidence interval; CVD=cardiovascular mortality; O3=ozone; PM2.5=fine particular matter with an aerodynamic diameter ≤2.5 μm
Fig 2
Fig 2
Percentage changes (central estimates and 95% confidence interval) in total, cardiovascular, and respiratory mortality associated with a 10 μg/m3 increase in PM2.5 and O3 in stratified analyses and in warm and cold seasons. Warm season is March to August for the northern hemisphere and September to February for the southern hemisphere; Cold season is September to February for the northern hemisphere and March to August for the southern hemisphere. P values for interactions were obtained from likelihood ratio tests. CI=confidence interval; CVD=cardiovascular mortality; O3=ozone; PM2.5=fine particular matter with an aerodynamic diameter ≤2.5 μm
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