Abstract
BACKGROUND: Emerging evidence has integrated short-term exposure to PM(1) with children's morbidity and mortality. Nevertheless, most available studies have been conducted on a daily scale, ignoring the exposure variations over the span of a day. OBJECTIVE: The main intention of this study was to examine the association between pediatric emergency department visits (PEDVs) and intra-day exposures to PM(1) and PM(2.5). We also aimed to investigate whether a high PM(1)/PM(2.5) ratio elevated the risk of PEDVs independent from PM(2.5) exposure within several hours. METHODS: We collected hourly data on aerial PM(1) and PM(2.5) concentrations, all-cause PEDVs, and meteorological factors from two megacities (i.e., Guangzhou and Shenzhen) in southern China during 2015-2016. Time-stratified case-crossover design and conditional logistic regression analysis were used to assess the associations of PEDVs with exposures to PM(1) and PM(2.5) at different lag hours. The contribution of PM(1) to PM(2.5)-associated risk was quantified by introducing PM(1)/PM(2.5) ratio as an additional exposure indicator in the analysis adjusting for PM(2.5). Subgroup analyses were performed stratified by sex, age, and season. RESULTS: During this study period, 97,508 and 101,639 children were included from Guangzhou and Shenzhen, respectively. PM(1) and PM(2.5) exposures within several hours were both remarkably related to an increased risk of PEDVs. Risks for PEDVs increased by 3.9% (95% confidence interval [CI]: 2.7-5.0%) in Guangzhou and 3.2% (95% CI: 1.9-4.4%) in Shenzhen for each interquartile range (Guangzhou: 21.4 μg/m(3), Shenzhen: 15.9 μg/m(3)) increase in PM(1) at lag 0-3 h, respectively. A high PM(1)/PM(2.5) ratio was substantially correlated with increased PEDVs, with an excess risk of 2.6% (95% CI: 1.2-4.0%) at lag 73-96 h in Guangzhou and 1.2% (95% CI: 0.4-2.0%) at lag 0-3 h in Shenzhen. Stratified analysis showed a clear seasonal pattern in PM-PEDVs relationships, with notably stronger risks in cold months (October to March of the following year) than in warm months (April to September). CONCLUSIONS: Exposures to ambient PM(1) and PM(2.5) within several hours were related to increased PEDVs. A high PM(1)/PM(2.5) ratio may contribute an additional risk independent from the short-term impacts of PM(2.5). These findings highlighted the significance of reducing PM(1) in minimizing health risks due to PM(2.5) exposure in children.