On Jul. 15, 2020, in collaboration with the Guangdong CDC, Hunan CDC, Sun Yat-Sen University and Southeast University, Professor Yuguo Li, Chair Professor of Building Environment, and his team at the Department of Mechanical Engineering of the University of Hong Kong (HKU), conducted a series of epidemiological and environmental studies on three important Covid-19 outbreak cases in Mainland China and Tokyo, and revealed that poor air ventilation plays a key role in its spread in indoor environments.