From Unofficial Stationeers Wiki
Pollutant, also known as X, is produced when smelting certain metals. A concentration of 0.1Mol or greater will cause your suit to warn about pollutants/poison in the air, and it's not recommended to breath air containing Pollutant.
Pollutant has a specific heat of 24.8 Joule / mol, making it great for using as a Coolant.
Pollutant has been noted as pure Chlorine, but can also be considered other hazardous gasses such as Hydrogen Sulfide, etc. This is why Volatiles are denoted as possibly being Chloromethane.
You can collect Pollutant from the following sources:
|Coal Ore||3 mol|
|Copper Ore||1 mol|
|Gold Ore||2 mol|
|Iron Ore||2 mol|
|Lead Ore||2 mol|
|Nickel Ore||1 mol|
|Silicon Ore||1 mol|
|Silver Ore||1 mol|
|Uranium Ore||35 mol|