Generally speaking, european emissions regulations are much stricter than the standards emplyed by *most* states. The EPA sets some general emission standards for the entire nation (regulating Mercury emissions, which Europe does not regulate) and some other heavy toxins. California and Pennslyvania regulate many other emissions, including visible particulates, allergens, carcinogens, and even noise (although usually noise emissions are restricted by city ordinance, not state law). Europe, on the other hand, has a very easily defined grouped emissions standard: not to exceed certain parts per million emissions of hydrocarbons, carbon monoxides, nitrogen oxides, in addition to visible grit and grime. Interestingly enough, in neither continent are airplane or oceangoing vessel's emissions regulated.