National Library of Medicine: N E Klepeis, W C Nelson, W R Ott, J P Robinson, A M Tsang, P Switzer, J V Behar, S C Hern, W H Engelmann.
"The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants."
,
2001,
https://pubmed.ncbi.nlm.nih.gov/11477521/.
We spend ~90% of our time indoors(Reported 2001)