The art of the characters will have these gas masks with a long filter tube leading to a canister on the pack.
The reason for these masks is when the fog was starting to get stronger these masks were what was used to breathe healthier air but are now practically useless against the fog but have become a cultural normalcy.
As the trains became the necessity for survival the conductors found themselves in a seat of power as they were the only ones who knew how to drive the trains. This enabled them to have nicer quarters and not have to do the hard labour the rest of the trains inhabitants have to do.