Oily, Blackened Pomegranates Courtesy of Metrolink?

We live 1,720 feet from a freeway according to the Los Angeles Times' interactive map, and yet our home is a mere 300 - 400 feet from where Metrolink idles and maintains its outdated diesel engines, the bulk of them Tier 0 (worst polluting). These are slowly going to be replaced by the new Tier 4 train but meanwhile, in the photo below. On the right, this is what a pomegranate from our backyard tree looks like before being washed and wiped free of the black, oily soot it has acquired from a season's growth. Stripes where the color of the fruit shows through were cleaned to show the contrast and thickness of the black soot layer.