Not sure what it is because the soot I have is just liquid that falls downwards and doesn't gather all around. Regardless, use liquid clay bar to get it off - anything above the clearcoat layer rubs right off (with a flipflop-on-wet-tile sound effect showing it does get in there good). I use it all the time on my rear aero kit and it's about 5-seconds of effort and leaves no marks. May take you 30 seconds though.

http://www.amazon.com/Turtle-Wax-T46...iquid+clay+bar

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'08 X5 3.0si - Alpine White / Saddle Brown interior
Specs: Sport Pkg, Premium Pkg, Tech Pkg, Comfort Access, Aero Kit, Style 433 staggered 20s on Conti DWS
Mods: Carbon 35 tint, LED angel eyes, GP Thunder 7500k fogs, H&R 20mm/25mm spacers, clear reflectors, gunsmoke-tinted taillights
Coded: Digital speedo, windows/sunroof/tailgate close via keyfob

X5 pics at Flickr