**Conflicts of interest**

For the NCPDIAC experiments, the Department of Hygiene, Kawasaki Medical School, obtained research funding from Sekisui House Ltd., Osaka, Japan, and from Yamada SXL Home (now known as Yamada Home) Co. Ltd., Takasaki, Japan. Additionally, the extra-porous charcoal paints were provided by Artech Kohboyu, Co. Ltd., Omura, Nagasaki, Japan. For the CCSNOP experiments, the Cosmic Garden Co. Ltd. provided the CCSNOP apparatus.
