Sure. But thats still very much a lower bound, and it makes a bunch of idealizing assumptions that are hopelessly overoptimistic (assuming your intake gets the full 400ppm of CO2, and you manage to extract all of it in one go).

Even from those numbers, you already get up to a football stadium of processed air per hour for every small town. For a big city, you need to process that football stadium worth of air every second.

Building infrastructure of that magnitude is a major commitment, and if most nations can not be arsed to replace a small number of fossil power plants per country, I honestly don't see us building large air processing plants in every single town in a timely manner (that are extremely likely to be less profitable than replacing the power plants).

What is the size of these process units?

Can it be coupled with current air processes?

Every house, office building and factory has air handling units.

Factories and other industrial sites also use compressors.