Mortality burden attributable to PM₁ in Zhejiang province, China

Limited evidence is available on the health effects of particulate matter with an aerodynamic diameter of <1 μm (PM₁), mainly due to the lack of its ground measurement worldwide.

To identify and examine the mortality risks and mortality burdens associated with PM₁, PM_2.5, and PM₁₀ in Zhejiang province, China.

We collected daily data regarding all-cause (stratified by age and gender), cardiovascular, stroke, respiratory, and chronic obstructive pulmonary disease (COPD) mortality, and PM₁, PM_2.5, and PM₁₀, from 11 cities in Zhejiang province, China during 2013 and 2017. We used a quasi-Poisson regression model to estimate city-specific associations between mortality and PM concentrations. Then we used a random-effect meta-analysis to pool the provincial estimates. To show the mortality burdens of PM₁, PM_2.5, and PM₁₀, we calculated the mortality fractions and deaths attributable to these PMs.

Daily concentrations of PM₁, PM_2.5, and PM₁₀ ranged between 0-199 μg/m³, 0-218 μg/m³, and 0-254 μg/m³, respectively; Mortality effects were significant in lag 0-2 days. The relative risks for all-cause mortality were 1.0064 (95% CI: 1.0034, 1.0094), 1.0061 (95% CI: 1.0034, 1.0089), and 1.0060 (95% CI: 1.0038, 1.0083) associated with a 10 μg/m³ increase in PM₁, PM_2.5, and PM₁₀, respectively. Age- and gender-stratified analysis shows that elderly people (aged 65+) and females are more sensitive to PMs. The mortality fractions of all-cause mortality were estimated to be 2.39% (95% CI: 1.28, 3.48) attributable to PM₁, 2.53% (95% CI: 1.42, 3.63) attributable to PM_2.5, and 3.08% (95% CI: 1.95, 4.19) attributable to PM₁₀. The ratios of attributable cause-specific deaths for PM₁/PM_2.5, PM₁/PM₁₀, and PM_2.5/PM₁₀ were higher than the ratios of their respective concentrations.

PM₁, PM_2.5 and PM₁₀ are risk factors of all-cause, cardiovascular, stroke, respiratory, and COPD mortality. PM₁ accounts for the vast majority of short-term PM_2.5- and PM₁₀-induced mortality. Our analyses support the notion that smaller size fractions of PM have a more toxic mortality impacts, which suggests to develop strategies to prevent and control PM₁ in China, such as to foster strict regulations for automobile and industrial emissions.