Smoke from coke mills contains not only particulates, but also chemical contaminants.

Having spent part of my youth seeing the glow from the coke mills of Gary, Indiana—and cleaning the black dust accumulation from the windowsills every month or so—I’m pleased OSHA has standards for emissions from coke mills.  The standard measurement method draws air samples through vials containing glass fiber filters, from which the trapped chemicals are extracted with benzene.  The benzene soluble fraction is measured with an analytical balance.  If it exceeds the limit, the sample is further analyzed with high-performance liquid chromatography for the presence of specific polynuclear aromatic hydrocarbons.