World consists of humans with primitive technology living within an asteroid space station built by their technologically advanced ancestors. A lot of knowledge has been lost, obviously.
The station has the interior square footage of Manhattan and is home to 300,000 humans. After generations of pilfering the station for materials, the station is mostly bare of technology, little more than a complex of ultra-durable habitats on the side of a rock with a bunch of iron age maniacs living inside. The space station consists mostly of large sun-lit greenhouse areas, originally parks but now used for cultivating food. If there was ever a source of artificial gravity, it no longer works, though thankfully these humans are genetically fortified against the delirious effects of microgravity.
Over time these humans have learned manage their air quality by managing the growth and decomposition of plants, avoiding combustion, and wicking away humidity with ceramic dew collectors*. The sun exposure of this rock can be adjusted post-hoc for whatever would make this scenario most plausible, but you can assume the base is built on Earth's moon as a default. The humans have access to the asteroid's rocky interior, where they might be mining ice (water, nitrogen, ammonia, etc.), tholin (space tar), metals, or whatever else might be useful in answering the question.
Re: plausibility comments. The station is built of futuristic "handwavium" as someone put it, so don't worry about that. These iron age humans started as a very small population in a massive greenhouse structure - managing their air quality would not be an issue until population increased. They would have time to adjust and learn as their situation became more difficult. Humans have learned how to thrive in some extremely hostile environments here on earth, living on ice sheets, deserts with single digit inches of rain per year, on floating rafts, and many other perilous places that require highly specialized survival skills. I have confidence that humans could learn to learn to live in what is essentially an enormous garden. I just need to figure out what that garden would have to look like to give them the best chance.
The air quality issue I've had the most difficulty understanding is temperature. My current understanding is that there is no need to actively heat a space station occupied by humans, because their body heat is sufficient. On the contrary, temperature control on a space station seems to be entirely about removing heat. On the ISS this is done by pumping liquid ammonia between the inside of the station and the exterior to radiate out heat.
How can my iron age human occupants manage the temperature of the station? An active solution, like bicycle-powered pumps feeding through the station's legacy radiators, is not preferred. Would it be possible for the station's original design to include a passive temperature regulation system in case of power failure? For example, could the station's air be channeled through long, finned tunnels of aluminum that created enough surface area with the (near) vacuum of space to cool the air? Perhaps the number of tunnels the air flows through is manually controlled to keep the air at the right temperature. And then what would create the airflow? If the uninsulated tunnels were colder than the rest of the station, could that create a natural passive airflow?
In addition to answering my question, I would appreciate references for further reading on this subject. More in-depth than the articles that come up on google. I don't really remember much physics, but I'm eager to learn if someone can tell me what area I should start looking at first.
*Note that the station does not need to be as dry as 21st century spacestations, because there are no longer any electronics.