I guess inserters produce so little pollution that the game just says 0?
I mean, if you load this save (
http://silverchat.com/~silver/factorio/3-101.zip ), you'll find 3 actual sources of pollution. One way to the NW in the oil field, a bunch of pollution around the pumps that flickers on and off as it dissipates pretty much as fast as it comes, and mystery pollution in the middle of the main line (presumably in some way related to those being the only 'purely stone/concrete' chunks)
What you don't see is pollution flickering on and off around the inserters, assemblers, or furnaces like you do around the pumps in the refinery.
I checked with F4->always show pollution values. If you examine the map with that on, the chunks not containing pumps (or in the mainline) do not even show up with numbers, despite being loaded with tons of inserters, assemblers, furnaces, roboports, and lights.
If everything were polluting while idle, I'd expect my whole base to flicker with pollution that dissipates quickly. What I'm asking is: why are pumps are so different from the other things? But, just to reiterate from my original post, it's not that I hate exceptions, nor do I "mind" per se, it's just a weird exception with no readily apparent explanation.
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edit: I know, I know: "I found your problem: your base is idle. you're not supposed to notice the pump thing because the rest of your base should be, you know, DOING something"
LOL, this save is after I let it run overnight while I slept