To investigate both short-term and long-term O3 exposures on school absenteeism due to health issues and the frequency of asthma-related symptoms, the UCLA investigators will conduct a study linking the CHIS 2011- 2019 data to daily O3 concentrations generated from the chemical transport model (CMT) developed by Dr, Michael Kleeman from UC Davis -California Institute of Technology (UCD-CIT), based on the respondents’ geo-coded residential addresses and interview dates. With the linked data, UCLA investigators will examine if the school absence and the frequency of asthma-related symptoms are associated with the short-term or long-term exposures to O3 after controlling for covariates and co-pollutants such as PM2.5 and NO2, and will conduct stratified and interaction analyses to identify whether the O3-related health effects are different by subpopulations such as race/ethnicity, gender, income, urban/suburban groups and by health insurance, asthma management status.