It's been brought to my attention that in Nigeria, cocoa is a very popular crop, lead-based gasoline additives are super popular, and cocoa has an unfortunate tendency to extract lead from the air and incorporate it into itself. The bad side of this is that Nigerian-grown chocolate is contaminated with lead. The good news is that I can use this to clean the air.
Cocoa isn't alone. Different kinds of plants take different chemicals out of the air. As an example, there's a type of daisy that extracts benzene from the air. If we plant these in the right combinations, we have perfectly clean air, no matter how much pollution nearby industries spew into it. You wouldn't want to eat the products of these plants, so we're not going to. Instead, we're going to chemically extract the pollution, much of which is industrially useful. Wait, what?
Lead, in air or paint, is a pollution, which mostly serves to give people who absorb it brain damage. But lead in a car battery is what gives it its range, and lead in a denistry apron is what makes it absorb radiation. Lead is mined in tons and tons a year, even though it only sells for 2 cents a pound. (The extraction process is cheap enough that even at that low price, a lead mine makes millions of dollars for its owners.)
Likewise, many other common pollution particles have a high industrial value. Benzene is useful as a solvent. A portion of smog is actually gasoline that managed to escape combustion. Formaldehyde, a common VOC, is useful in the paper and textile industries. (it's a precursor chemical there. The final chemical bears little resemblance.)
After the extraction is done, we'll be left with a wet slurry of plant goo. We can throw this away. Or we could grow pretty flowers in it. You know, whichever.