I felt the 1 pollution per minute was a bit cheaty. Could you make a setting or default for increasing pollution?

I added this block to mine for example (similar in each big machine), before the crafting speed and energy usage were set:

    if bigassembly.energy_source and bigassembly.energy_source.emissions_per_minute then
      local prepollution = bigassembly.energy_source.emissions_per_minute
      bigassembly.energy_source.emissions_per_minute = bigassembly.energy_source.emissions_per_minute * (speed / bigassembly.crafting_speed)
      log("adjusted pollution of bigassembly from "..prepollution.." to "..bigassembly.energy_source.emissions_per_minute)
    end

Sorry it took me so long, but I have now incorporated your code into version 0.3.4. Thanks so much for the suggestion and the code!