Associations between PM₁ exposure and daily emergency department visits in 19 hospitals, Beijing

Although the adverse health effects caused by PM_2.5 (particulate matter (PM) with an aerodynamic diameter <2.5 μm) and PM₁₀ (PM with an aerodynamic diameter <10 μm) have been examined in numeric studies, far less scientific evidence is available for PM with an aerodynamic diameter <1 μm (PM₁). We performed a time series analysis to elucidate the associations between PM₁ exposure and emergency department visits (EDVs) in 19 hospitals within Beijing. During the study period from January 2016 to December 2017, the average PM₁ (mean ± standard deviation) was determined to be 39 ± 39 μg/m³, which was approximately 36% lower than that of 61 ± 56 μg/m³ for PM_2.5. Results based on meta-analysis suggest that non-accidental and respiratory EDVs increased by 0.47% (95% confidence interval, CI: 0.35, 0.59%) and 0.59% (95%CI: 0.38, 0.8%) per 10 μg/m³ uptick in PM₁ exposure. By comparison, the magnitude downgraded to 0.27% (95%CI: 0.15, 0.39%) in non-accidental and 0.32% (95%CI: 0.18, 0.47%) in respiratory EDVs for PM_2.5 exposure, indicating that PMs of a smaller size may be a higher risk factor for EDVs. No significant differences in PM-associated EDV effects were noted between males and females, while stratified analysis by age and season illustrated that stronger effects were found for a warm season and young population. Our analysis reinforces the notion that PM₁ exhibited a higher risk for EDVs, suggesting more efforts may be required to mitigate PM₁ pollution.