[southern_cross]

Conveniently not mentioned is this article is the fact that normal CO2 concentrations in human lungs are about 40,000ppm - or about 100x higher than current background levels, and many times higher than the elevated levels mentioned in this article. And I don't know about you, but when I'm in a crowded room what eventually makes me tired and uncomfortable is the heat and humidity from all those bodies. Turn on the AC (which reduces both heat and humidity) and I will be feeling much better in short order.

[annamargot]

Is the AC not also helping to circulate the air, removing some of the CO2?

[southern_cross]

It would depend on the situation. For a single room system, generally no; for a multi-room system, generally yes if the other rooms are empty or at least relatively less crowded than the one you're in. That is, I wouldn't expect the AC to really remove any CO2; it might redistribute it, though.

[rusticpenn]

The exhaust for ACs are generally outside the room, so there is an airflow..

[southern_cross]

Heat dumping is done outside the room, of course, but that's a separate airflow, one that's generally disconnected from the room. The cool AC flow itself is usually a closed cycle of some sort. You would be kind of defeating the whole purpose of trying to cool and dehumidify the air if you did otherwise, plus your AC system might have to run continuously in order to get anything done. There will always be some leakage, of course.

[QuickToBan]

The use of AC increases CO2 indoors, doubling or tripling it. Measuring is how I know. AC decreases ventilation.