In recent ve years, air quality in China has been gradually improved; however, the prevalence of asthma in China has still increased signi cantly. This study aims to examine whether air pollution exposure is a signi cant contributor to childhood asthma and to explore the mechanisms using exposure and response biomarkers. Methods The generalized additive model was applied to evaluate the effects of air pollutants on asthma hospitalization. Urinary 1-hydroxypyrene (1-OHPyr) was determined as PAHs

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... exposure biomarker. Metabolic pro les and microbial diversity were screened and selected as response biomarkers. Results Daily average concentrations of the six common air pollutants were not signi cantly associated with daily childhood asthma hospitalization. Urinary 1-OHPyr level showed large variability among asthmatic children and were positively correlated with the abundance of Prevotella (genus level) and purine metabolism. Conclusions The biomarker of PAHs exposure is associated with metabolic and microbiological biomarkers of childhood asthma. As the potential health risk, we suggest that PAHs should be included in the national monitoring system aiming to reduce the exposure.