Last fall, black dust began to blow through residential neighborhoods on the southeast side of Chicago. Only it wasn't really dust; it was a fine black residue that clung to everything it touched, including noses and throats. Residents eventually learned that it was an oil byproduct called petroleum coke — petcoke for short — and it was being stored in massive uncovered piles at facilities owned by the Koch brothers. VICE News's Danny Gold traveled to Chicago to see what happens when clouds of toxic oil dust blow through the Windy City.