https://www.mouser.com/datasheet/2/682/Sensirion_Gas_Sensors...
https://thinkprogress.org/exclusive-elevated-co2-levels-dire...
> Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers: A Controlled Exposure Study of Green and Conventional Office Environments
> ... Methods: Twenty-four participants spent 6 full work days (0900–1700 hours) in an environmentally controlled office space, blinded to test conditions. On different days, they were exposed to IEQ conditions representative of Conventional [high concentrations of volatile organic compounds (VOCs)] and Green (low concentrations of VOCs) office buildings in the United States. Additional conditions simulated a Green building with a high outdoor air ventilation rate (labeled Green+) and artificially elevated carbon dioxide (CO2) levels independent of ventilation.
> Results: On average, cognitive scores were 61% higher on the Green building day and 101% higher on the two Green+ building days than on the Conventional building day (p < 0.0001). VOCs and CO2 were independently associated with cognitive scores.
> Conclusions: Cognitive function scores were significantly better under Green+ building conditions than in the Conventional building conditions for all nine functional domains. These findings have wide-ranging implications because this study was designed to reflect conditions that are commonly encountered every day in many indoor environments.
The overall feeling I got was "tired". My eyes didn't want to stay open. My mind felt like gauze was wrapping it. My attitude was mellowed and slightly depressed. It took more effort to move (even to walk to the door outside, which I did often despite it being allergy season). As soon as I spent 10m outside my energy started to return.
I can’t imagine if the whole office was filled with people exercising.