That's true: diesel engines generally have higher mpg and lower CO2 emissions than gasoline. Problem is they emit higher levels of nitrogen oxide (ask Volkswage

That's true: diesel engines generally have higher mpg and lower CO2 emissions than gasoline. Problem is they emit higher levels of nitrogen oxide (ask Volkswagen) which beside being a greenhouse gas also poisons the environment. Presumably newer cars with Adblue systems which greatly reduce the amount of emitted NOX could be better for the environment than gasoline powered cars.