Method for removing surface deposits of concentrated collected particles

Apparatus for separating and collecting particulates entrained in a flow of fluid, said apparatus comprising:

• (a) a virtual impactor capable of separating a fluid stream into a major flow and a minor flow, the major flow including a minor portion of particulates that are above a predetermined size and the minor flow including a major portion of the particulates that are above the predetermined size, said virtual impactor including a minor flow outlet through which the minor flow exits the virtual impactor;
• (b) at least one collection surface disposed adjacent to said virtual impactor, such that the minor flow of fluid moving through said minor flow outlet is directed toward said at least one collection surface;
• (c) a prime mover drivingly coupled to one of said virtual impactor and at least one collection surface, causing a relative position of said virtual impactor and said at least one collection surface to be selectively changed over time, so that the minor flow of fluid moving through said minor flow outlet is directed, over time, towards one of a different portion of a specific one of said at least one collection surface, and a different one of said at least one collection surface;
• and
• (d) means to collect a sample from said at least one collection surface.