This photographer has done a fine job of creating a photographic analysis of an anomaly over Washington DC. There is no question of hoax here, or of a misidentification. This material is unidentified. Whether or not it could be identified as some sort of airborne pollutant or extremely lightweight floating debris is another question. However, some of the transformations that take place are very fast, which only adds to the high strangeness.

Story Source:
http://www.ufodc.com/page%2013.html