Having had the cockpit fill with smoke/fumes on rotation recently, I can confirm that an Eros mask on 100% is pretty effective at keeping the nasties out
I flew with a gent who, after 2 go-arounds, thought he was in need of a cigarette. I said, "Do whatever you need to do to get us on the ground." I put on the mask, and I could still smell the smoke. EMER kept the smoke out better.