You can just plop these tanks where it's needed and move them around. And they occupy a smaller space than an equivalent tree would. (By equivalent I mean the size of tree needed to produce oxygen and take co2 by volume take much more space than this tank). You can read more about this tech here: https://liquid3.rs/about/

Just to repeat myself again. These are not meant to replace trees but to help with air pollution in places where there's no place for more trees or *where trees can't even grow to an appropriate size* exactly due to air pollution.