Background Ambient fine particulate matter with aerodynamic diameter less than 2.5 µm (PM2.5) has been associated with deteriorated respiratory health, but evidence on particles in smaller sizes and childhood respiratory health has been limited.
Methods We collected time-series data on daily respiratory emergency room visits (ERVs) among children under 14 years old in Beijing, China, during 2015–2017. Concurrently, size-fractioned number concentrations of particles in size ranges of 5–560 nm (PNC5–560) and mass concentrations of PM2.5, black carbon (BC) and nitrogen dioxide (NO2) were measured from a fixed-location monitoring station in the urban area of Beijing. Confounder-adjusted Poisson regression models were used to estimate excessive risks (ERs) of particle size fractions on childhood respiratory ERVs, and positive matrix factorisation models were applied to apportion the sources of PNC5–560.
Results Among the 136 925 cases of all-respiratory ERVs, increased risks were associated with IQR increases in PNC25–100 (ER=5.4%, 95% CI 2.4% to 8.6%), PNC100–560 (4.9%, 95% CI 2.5% to 7.3%) and PM2.5 (1.3%, 95% CI 0.1% to 2.5%) at current and 1 prior days (lag0–1). Major sources of PNC5–560 were identified, including nucleation (36.5%), gasoline vehicle emissions (27.9%), diesel vehicle emissions (18.9%) and secondary aerosols (10.6%). Emissions from gasoline and diesel vehicles were found of significant associations with all-respiratory ERVs, with increased ERs of 6.0% (95% CI 2.5% to 9.7%) and 4.4% (95% CI 1.7% to 7.1%) at lag0–1 days, respectively. Exposures to other traffic-related pollutants (BC and NO2) were also associated with increased respiratory ERVs.
Conclusion Our findings suggest that exposures to higher levels of PNC5–560 from traffic emissions could be attributed to increased childhood respiratory morbidity, which supports traffic emission control priority in urban areas.
- clinical epidemiology
- respiratory infection
Data availability statement
Data are available upon reasonable request. We collected daily data on hospital emergency room visits for respiratory diseases between July 2015 and June 2017 from Beijing Children's Hospital.
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JF and XS contributed equally.
Contributors WH and BX: concept and design, critical revision of the manuscript for important intellectual content, obtainment of funding and supervision; had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. JF and XS contributed equally and are cofirst authors of this article, and drafted the manuscript. Acquisition, analysis or interpretation of data: JS, RW, HX, YZe and XX. Statistical analysis: JF, HX, RW, TW and NY. Administrative, technical or material support: XS, JJ, YZh and YX.
Funding This work was supported by National Key Research and Development Project (2017YFC0211701 and 2016YFC0901103) and China National Natural Science Foundation (21190051).
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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