Well ... there are projects for artificial trees processing CO2 in city agglomerates ... so i say : Grass shaped active nanotech-filters in ferromagnetic composite matrix on an magnetized ground layer.
THIS WAY, WE BUILD THE FUTURE TO THE WEIRDEST HUMAN IMAGINATIONS !
... FINALLY POSSIBLE ! ..... powered by EMTG.
P.S.: The magnetized ground layer is programable - you can make the grass change heights, dance and form complex forms known from magnetic-liquids. Sell off at 120 bucks/square meter. It also forms waves like water when cars drive down the road.