Recently, the National Health Commission released the guidelines for health protection of people with air pollution (haze). The guidelines proposed that air purifiers should be equipped in indoor places such as kindergartens, primary and secondary schools, offices and indoor fitness places to minimize PM2 5 concentration; If possible, fresh air can be introduced by fresh air device to prevent excessive carbon dioxide concentration. In severe haze weather, kindergartens and schools shall suspend outdoor collective activities and try to avoid indoor sports.