I don't know if this is a similar product to what Dee was referring to, but I've used this on refrigeration condenser
coils :
Cal-Spray Evap Foam
(www .nucalgon.com/products/aerosol_evapfoam.htm)
Nu-Calgon
(www .nucalgon.com) makes all kinds of acid/alkali cleaners for HVAC and refrigeration systems
(www .nucalgon.com/products/products.htm).
The Cal-Spray Evap Foam that I've used works very well on condensers that are caked with grease (cooking grease) and dust/dirt. I don't know how any of Nu-calgon's products will work on the black atomizer coil buildup. I also have no idea how safe these would be to use for our purposes, but Nu-Calgon provides a MSDS for each of their products on the website.
Keep in mind that some of the products listed there are made for commercial ice-makers, so they might have a product that will work for our needs... If this buildup is similar to scale, maybe this could be of use? : Liquid Ice Machine Cleaner
(www .nucalgon.com/products/iceMach_filtration_liquidicemachcleaner.htm)
(Sorry about the goofy link mess that this post is. But, I can't post normal links yet.)