I wonder what famous Dutch hydraulic engineers and their environmental science counterparts would say about removing natural water absorption in favour of promoting runoff over chemical-laden surfaces. Similarly, I wonder if we shouldn't look at such substances from the perspective of the overall energy expended on their production, installation, maintenance and eventual disposal over time.
The question isn't concrete vs. some environmentally friendly surface, the question is concrete vs. smog-eating concrete, and whether the smog-eating concrete is more environmentally friendly than regular concrete. Yes, total cost to the environment over time is a consideration here.
If you choose to artificially limit your scope of thought, then by all means go ahead. However, any conclusions based upon such thinking will be similarly limited. Personally I find more interest and utility in analyzing the potential interactions of things on a broader scale.
There is some parallel here in conventional computing wisdom: measure twice cut once dictates that, given limited time, you're better off thinking a course of action out before investing effort in creating something requiring an ongoing investment of effort.
Thus, if the scope for this type of invention is environmental quality, why not consider overall energy use and knock-on effects as part of your evaluation?
I believe I just wasn't clear. In my first sentence I was clarifying the discussion - we agree that no concrete at all is best if possible. In my second sentence I was agreeing that it makes sense to consider energy use before rolling out the supposedly greener concrete.
