The investigators will collect the data of outpatient and emergency children in Beijing Children's hospital and other participating hospitals due to respiratory diseases from 2010 to 2021, , collect clinical data and basic information, obtain air pollution data and meteorological monitoring data and perform data processing and statistical analysis,，then analyzes the impact of air pollution on children's respiratory diseases.
The investigators expect to reveal the association between air pollution and childhood respiratory diseases through a multi-center observational study, and summarize the relationship between air pollution and childhood respiratory diseases.