I thought it was common knowledge. Here’s some information from the Environmental Protection Agency:

> Americans, on average, spend approximately 90 percent of their time indoors,1 where the concentrations of some pollutants are often 2 to 5 times higher than typical outdoor concentrations

There’s been so much research on this by so many different organizations around the world, as far as I’ve known almost everybody was aware of this as fact.

There is an extraordinary amount of data online about this, should be easy to find. On average, outdoor air is healthier than indoor air, often by a wide margin. The above is from the EPA site: https://www.epa.gov/report-environment/indoor-air-quality

Also https://www.cnbc.com/2016/04/22/indoor-air-can-be-deadlier-t...

> indoor air is significantly more polluted in MOST cases

> indoors [...] concentrations of SOME pollutants are OFTEN [...] higher

Those two statements don't seem to be the same to me?

Everyone can make their own decisions about how much time they want to spend outdoors versus indoors. I encourage you to do the research yourself if it’s important to you, and make appropriate lifestyle choices. From the second link:

> World Health Organization has said that household cooking with coal or biomass-burning stoves led to 4.3 million deaths in 2012, compared with 3.7 million deaths from outdoor air pollution.

And that’s just talking about one of many different sources of pollution. There are so many sources of pollution indoors, sources that are very close to you physically, that you should carefully consider these factors and the statistics surrounding them.

For example, I don't live in a country where "household cooking with coal or biomass-burning stoves" is even a thing. I have an induction stove. In fact the air outside of my house is almost certainly worse because of a nearby highway.

Again, you are focusing on one specific source as an example. Feel free to ignore a decade of research on this topic -- but it's worth getting informed IMO.