Hmmm... Buffalo NY? I can bet a majority of that dust would be salt, as there is a couple of Salt Mines in both the US & Canada within 200 miles - Dust Travels. The rest would be iron oxide from Detroit car manufacturing. And the rest would be crap (lint, smoke, carbon from the smoke, and who knows.) Since it is salt as I believe, it will need a double bath or a bath with a double rinse to make sure the salt comes off. And dry it quickly with compressed air, heat gun or hair dryer set on high and hot. Salt and water will make it corrosive, so you want it off and as squeaky clean as possible.

Use warm distilled water.

If when it dries you get white lines between pads and traces, you need to wash it again as the salt did not get come off completely. (and if it is Tap water, its adding to the salt as it as salt in it as well from its chlorination process. This is why you use distilled water.)