So I'm trying to develop a world that's very inhospitable to my characters (humans.) And I'm looking for a some sort of fine dust that is naturally occurring but deadly if inhaled after about a day of breathing it in. This threat would have to be easily nullified with a dust mask.
The world itself is Cold (about -10 degrees F.) It has a lower gravity but a slightly thicker atmosphere than Earth (about 2 atm.) This dust would be found everywhere.
Currently I'm using fine sulfur dust.
Any good alternatives? And if so what effect would it have on a snowy landscape?