Concentration-Response Relationship between PM(2.5) and Daily Respiratory Deaths in China: A Systematic Review and Metaregression Analysis of Time-Series Studies

The association between the particulate matters with aerodynamic diameter ≤ 2.5 μm (PM(2.5)) and daily respiratory deaths, particularly the concentration-response pattern, has not been fully examined and established in China. We conducted a systematic review of time-series studies to compile information on the associations between PM(2.5) concentration and respiratory deaths and used metaregression to assess the concentration-response relationship. Out of 1,957 studies screened, eleven articles in English and two articles in Chinese met the eligibility criteria. For single-day lags, per 10 μg/m(3) increase in PM(2.5) concentration was associated with 0.30 [95% confidence interval (CI): 0.10, 0.50] percent increase in daily respiratory deaths; for multiday lags, the corresponding increase in respiratory deaths was 0.69 (95% CI: 0.55, 0.83) percent. Difference in the effects was observed between the northern cities and the south cities in China. No statistically significant concentration-response relationship between PM(2.5) concentrations and their effects was found. With increasingly wider location coverage for PM(2.5) data, it is crucial to further investigate the concentration-response pattern of PM(2.5) effects on respiratory and other cause-specific mortality for the refinement and adaptation of global and national air quality guidelines and targets.