I really, really hate the idea of pollution the way Pyure is suggesting it as an indescript efficiency-cutting variable. It's not even just about realism, it straight up makes no sense and seems to be about making the implementation super-easy and not balanced, practical, or realistic. Very few machines are affected by pollution because they literally don't interact with it in any meaningful way. Pollution is not a logistic problem, it's an ecological one. The majority of effects should only affect players and animals. IE, a sufficient level of pollution would cause reduced sunlight, making solar boilers and solar panels produce less and less power as it worsens. At a certain level, rain would become acidic, damaging any living thing that the rain touches that isn't wearing a hazmat suit. Bad enough and it even damages the hazmat suit until it melts and hurts you. Think 'Twilight Forest' in how the acid rain works, except not block-piercing. Sufficient pollution levels would also randomly replace water source blocks with 'polluted water' source blocks, which would calcify or mess with machines. IE, if a boiler gets it, it would reduce the fuel value by 50% and also the steam value by 25%, making for a grand old fucking. This is the most painful impact I can see, besides acid rain. Polluted water getting into an ore washer would make it take 5 times as long to wash. In a autoclave, it would outright be unable to function at all. Cleaning the water would involve a new machine, a Filter Unit which would use filters made of wool and carbon fiber which would suck up, say, 16 liters of Pwater and produce 12 liters of regular water, with a chance of byproduct of dirt, dark ash, and tiny sulfur. The filter would wear down durability with each successive use, making it an expensive process to repeatedly clean water.
Lastly, a high enough level of pollution would blanket the area with Radioactivity I to IV, requiring constant careful use of a hazmat suit to even traverse. Machines which use mufflers would, in addition to outputting pollution, also work slower and slower (without using any less power) as it presumed muffler = output thus they require an air input and smeggy air is less effective. It would also make machines that require maintenance, require it more and more quickly, since the acidic humidity and air would corrode the machine (such as sulfuric and nitric compounds do IRL)
Huge bonus idea: Rarely, random chunks/areas can spawn with pre-existing pollution levels. Could be a fun idea to have a new biome, 'Nuclear Wasteland' with a permanent Radioactivity I. :3
Cleaning pollution, besides going away super-slow by itself, could involve building a multi-block machine Air Purifier. It uses a 3x3 grid of filters to make Filter Blocks in a star shape (3x3x3) surrounded by casings, the speed affected by power level (starting with 8v for the slowest), and extracting dirt, carbon, and dark ash from the air for slowest effect, or the option to build one for water (or one for each, but not both!) which will produce dirt, dark ash, sulfur, and sulfuric acid (as a liquid, in tiny amounts) from Pwater. If it gets only regular water, it will produce dirt only, at a very low (1%?) rate, and outputs regular water again. (In that way it could be an infinite dirt generator, but at the speed/voltage ratio, it would be an awfully expensive, awful way!)
In polluted settings, the above water-filter process would be required to have reliable, non-polluted water. All your water would have to pass through one or an array of them to even be useable. This, I feel, is a painful restriction that makes pollution a very big concern. (Or in my case, a goal! Make a sufficiently functional factory in a smog bowl! YAY MEXICO CITY!)
I hope you like my ideas. I feel it marries balance and utility with realism and logistics in the true spirit of Gregtech without being overly redundant or being too radically different from 'pollution hurts productivity'.
Also, semi-unrelated: I always wondered why there's no ash output from large boilers. Where it go??? I likey my mountain of ash blox!