There are multiple studies on the issue, and another user linked to Wikipedia. I'd personally recommend buying a CO2 monitor: https://www.aliexpress.com/item/3

There are multiple studies on the issue, and another user linked to Wikipedia. I'd personally recommend buying a CO2 monitor: https://www.aliexpress.com/item/32887534678.html?spm=a2g0o.productlist.0.0.ad21e803I1BRqT&algo_pvid=a6f15dbf-97bc-4346-a5f3-9efd5a46e35e&algo_expid=a6f15dbf-97bc-4346-a5f3-9efd5a46e35e-0&btsid=0ab50f0815827071300405942e7277&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_ https://www.aliexpress.com/item/32887534678.html?spm=a2g0o.p...