Background

Under-5 mortality rate is an important indicator in Millennium Development Goals and Sustainable Development Goals. To date, no nationally representative studies have examined the effects of fine particulate matter (PM_2.5 ) air pollution on under-5 mortality.

Objective

To investigate the association of short-term exposure to PM_2.5 with under-5 mortality from total and specific causes in China.

Methods

We used the national Maternal and Child Health Surveillance System to identify under-5 mortality cases during the study period of 2009 to 2019. We adopted a time-stratified case-crossover study design at the individual level to capture the effect of short-term exposure to daily PM_2.5 on under-5 mortality, using conditional logistic regression models.

Results

A total of 61,464 under-5 mortality cases were included. A 10 μg/m³ increase in concentrations of PM_2.5 on lag 0-1 d was significantly associated with a 1.15% (95%confidence interval: 0.65%, 1.65%) increase in under-5 mortality. Mortality from diarrhea, pneumonia, digestive diseases, and preterm birth were significantly associated with exposure to PM_2.5 . The effect estimates were larger for neonatal mortality (<28 days), female children, and in warm seasons. We observed steeper slopes in lower ranges (<50 μg/m³ ) of the concentration-response curve between PM_2.5 and under-5 mortality, and positive associations remained below the 24-h PM_2.5 concentration limit recommended by WHO Air Quality Guidelines and China Air Quality Standards.

Conclusions

This nationwide case-crossover study in China demonstrated that acute exposure to PM_2.5 may significantly increase the risk of under-5 mortality, with larger effects for neonates, female children, and during warm seasons. Relevant control strategies are needed to remove this roadblock to achieving under-5 mortality targets in developing countries.