How long have you had the new bow? It's possible that it was over-rosined at the shop. When a bow is rehaired, many luthiers add some powdered rosin to allow the bow to pick up rosin from a rosin cake more easily. I normally expect my bow to produce more dust than usual for the first two or three days after being rehaired. If it's excessive, there may be extra dust for as long as a week or two.