Thank you all for explanation, I really didn't do at least one more experiment with speed module. Now I've checked that inserted speed module also increases pollution production (it's not mentioned in description) and efficiency module decreases it, what proofs that pollution production linearly ...

Description of productivity module says that they produce +5%/+7%/+10% more pollution when the actual numbers are ~50%/70%/...

Check on screenshots for assembly machines 2 and 3: all of them have same receipt and different sets of productivity modules. When assembly machine 3 has basic pollution ...