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Predicting influence of human thermal plume on the diffusion of respiration-produced particles is an important issue for improving indoor air quality through eliminating infectious microbes efficiently. In this study, the Large Eddy Simulation was utilized to predict the effects of thermal plume of different intensities on particle diffusion. Three postures of the human body model and three room temperatures were considered. The results show that the convective heat transfer coefficient on the surface of the human body varies greatly with different postures. The coefficient is the largest when the model is in sitting posture, leading to the greatest heat transfer rate. Meanwhile, the thermal plume generated by bending the thigh increases the size of the facial thermal plume in horizon direction. The increase of the difference between indoor temperature and skin temperature causes an increase of the convective heat transfer of the manikin, leading to stronger airflow in front of the face. The thicker and faster the human thermal plume is, the more difficult it is penetrated by aerosols produced by nasal breathing, finally resulting in most particles distributed within 0.2 m thick under the roof.

The ventilation modalities in most Chinese residences are infiltration and opening windows. We measured infiltration rates and air change rates at night, with no attempt to change occupants' behaviors, of urban residences in five climate zones of China during four seasons. Using the CO 2 decay method, we found the median infiltration rate for 294 residences to be 0.34 h −1 . Using occupant-generated CO 2 as tracer gas, we determined air change rates over the course of 1 year in 46 bedrooms at night from mass balance considerations. In 54% of the measurements, windows were closed, so ventilation was only by infiltration. Windows were mainly closed when the outdoor temperature was below 15°C and above 26°C. The median infiltration rates did not differ appreciably among seasons and climate zones and were always less than 0.45 h −1 .

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The indoor environment influences occupants' health. From March 1, 2018, to February 28, 2019, we continuously monitored indoor temperature (T), relative humidity (RH), and CO 2 concentration in bedrooms via an online system in 165 residences that covered all five climate zones of China. Meanwhile, we asked one specific occupant in each home to complete questionnaires about perceived air quality and sick building syndrome (SBS) symptoms at the end of each month. Higher CO 2 concentration was significantly associated with a higher percentage of perceived stuffy odor and skin SBS symptoms. Higher relative humidity was associated with higher percentage of perceived moldy odor and humid air, while lower RH was associated with a higher percentage of perceived dry air. Occupants who lived in residences with high RH were less likely to have mucosal and skin SBS symptoms (adjusted odds ratio (AOR): 0.73-0.78). However, the benefit of high humidity for perceived dry air and skin dryness symptoms is weaker if there is a high CO 2 concentration level. K E Y W O R D SCO 2 , home, odors, perceived dry air, relative humidity, sick building syndrome | 1019 HOU et al.

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