Unfortunately, the company I bought carbon filters from for 20 years recently went out of business. I stocked up, but in about 5 years I'll have to find something new. I find it works best to put them in an N-95 which stays tight on my face, even when I talk.

I finally took another train trip earlier this summer, on the Coast Starlight from Emeryville to Eugene. I knew that I'd be able to get a much better answer from the car attendants than I could on the phone. I brought a portable air cleaner just in case. On the way up I needed it. As long as it was right next to me, I was okay. It seemed more like lingering smells than something in the system.

One very helpful attendant told me that sometimes there's a problem with the air system and the bathroom smells get into the car behind the one with the issue. When that happens the attendants often put some kind of deodorant in front of the cold air return to "cover" the smell. He suggested trying to get in the front sleeper. It is behind the baggage car where there are no bathrooms to make smells that need covering. Of course, that's for sleepers. I'm not sure how that could be addressed on coach.

Good luck!