I think the plastic bumper on base model holds lime rock and other light colored road dust. (truecar.com)
Whatever this rogue or hero in disguise is looking for, is his private business and in the hands of the author to reveal it's secrets one layer of road dust at a time. (bookcovers.io)
The source we identified as road dust had most common soil elements as well as high amounts of ogarnic carbon, elemental carbon and sulfur. (realclimate.org)