If plants are similar to humans in that increased air cycling would correspond to increased moisture cycling, I wouldn't look toward such slow growing plants as Sans for doing much for the air. Doesn't it seem like a plant would have a slow overall metabolism, or whatever that would be called for a plant, if it is one known for not needing/using much moisture? If that's a realistic thing, then it makes sense that the Sans aren't at the top of any "air cleaning ability" list because Sans use water so much more slowly than so many other plants. They're not cacti, by far, but sooooo many other plants need so much more water. These thoughts could be far from reality, just going with gut instinct theory.
