once 2.x drops do not expect new 1.x mods from me, mods will be slowly ported based on my needs and/or requests from the community, thx for playing!

Use the new shortcut to drag over an area containing polluting entities, and on release it'll tell you how many air purifiers (rounded up) the area needs.

Dragging in alt-mode will include any purifiers, so you can see how many you still need (or overplaced).

The mod will assume that you only use the basic tier filter. (as will the mod suggested below, no support for advanced filters in either currently)

Use together with https://mods.factorio.com/mod/kr-air-purifier-helper in order to be able to nicely integrate them into designs without worrying about io.