Given how carcinogenic coal dust is, this will be natural selection in action.
its only called rollin coal... doesnt have anything to do with coal mate 
just a case of modifying the air to diesel mix to create the black smoke...
as for environmentalists that jump up and down about the polution - 8 reasons why diesel engines are better than petrol engines....
1. Diesels are more efficient. Most gasoline engines convert about 30 percent of their fuel energy into actual power. A traditional diesel converts about 45 percent. And advanced diesels can hit about 50 percent.
2. Diesels are more reliable. Because they don’t need high-voltage ignition systems, diesel engines never fail for lack of a spark. They also don’t emit radio frequency emissions that can interfere with a vehicle’s other electronic systems.
3. Diesels run cooler. Because they are more efficient, diesel engines release less waste heat while in operation.
4. Diesels last longer. Diesel engine parts are generally stronger than gas engine components, and diesel fuel has superior lubricating properties. As a result, diesel engines tend to last twice as long as gas-powered ones.
5. Diesel fuel is safer. Diesel fuel doesn’t release fumes like gasoline does. It’s more difficult to burn and won’t explode like its lighter counterpart.
6. Diesels are more easily turbo-charged. Put under sufficient pressure, gasoline engines will spontaneously detonate. By contrast, the amount of super- or turbo-charging pressures diesel engines can endure are limited only by the strength of the engines themselves.
7. Diesels produce minimal carbon monoxide. This makes diesel generators useful in mines and submarines, environments in which gasoline engine exhaust would prove deadly.
8. Diesel engines can easily accept synthetic fuels. Non-petroleum-based biofuels will run easily in diesel engines, whereas gas engines need to be significantly modified to accept such alternative fuels.
