Excerpts from the United State Environment Protection Agency (EPA) web site:
"Research indicates that people spend approximately 90 percent of their time indoors"
"EPA's studies found levels of about a dozen common organic pollutants to be 2 to 5 times higher inside homes than outside, regardless of whether the homes were located in rural or highly industrial areas."
Findings of a study commissioned by the UK Clean Air Day campaign in 2019:
"Indoor air pollution is over three times worse than outdoor air pollution, with campaigners calling UK households ‘toxic boxes’ due to the number of air pollution particles trapped inside."