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

Although the adverse health effects caused by PM2.5 (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 PM2.5. 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 PM2.5 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.