Alteration to the Air Filtering mod by Schorty! This mod makes it so the upgraded versions of the Air Filtering Machine remove pollution in a radius making them much more effective at pollution control.
https://mods.factorio.com/mod/air-filtering

This alteration is inspired by Better Air Filtering by JoeyDP (https://mods.factorio.com/mod/better-air-filtering). The mod made it so the mk2 and mk3 air filtering machines would start removing pollution in a larger chunk radius instead of just the chunk that the machine is placed in. The mk2 and mk3 still removed more pollution but would also each have a larger radius from the last machine respectively.

My variation of Air Filtering does much of the same, however, probably not quite as cleanly as I'm no coder. Nonetheless, it works and I believe I've balanced it well:

The MK1 Air Filtering machine still removes 180 pollution per second from its chunk.
The MK2 Air Filtering machine removes 480 pollution from its chunk and then 50 pollution from 1 chunk in each cardinal direction (which results in a total of 680 pollution total per second).
The MK3 Air Filtering machine removes 2400 pollution from its chunk and then 100 pollution from 2 chunks in each cardinal direction and 1 chunk diagonally (which results in 3600 pollution total per second).

I played a lot with these numbers (originally the surrounding chunks were set to remove a lot more pollution than just 50 and 100) but ended up deciding that they were too overpowered until the numbers were much lower. At first you could place a mk3 machine, but once it was powered and had a filter it would almost instantly remove all the pollution in its radius. I wanted it to be more of a gradual effect, so I slowed it down.