Maybe you should inform US Steel (Now USX) about it. People in Pittsburgh, PA should be warned that the USX Corporate Headquarters skyscraper, downtown, is an enviornmental hazard since it is primarily constructed of the stuf.. :)
If I remember the stories correctly, the people were fully aware of the problem because they had this stuff raining on them continually. I think that the company eventually put a clear coating over the exposed Cor-Ten. The coating made the steel appear to be just what was orginally designed, but it prevented further oxidation and the subsequent rain of rust particles.
Bill