In an ideal libertarian world, pollution and corporate environmentalism could be handled in the free market, with free-thinking, empowered consumers simply driving the nasty companies out of business. But ours has been a very slanted economy, as regards health and pollution. Government has fully co-sponsored the rise of petrofuels over the past 100 years, and has fully cooperated with the related industries to ensure their success, prosperity, and sustainability. So, I say if you want a full-on libertarian free market, fine. But I think it would be irresponsible to do so without setting a level playing field, i.e. one that does not allow for the degradation of others' property or life.
Air belongs to everybody.
It is my air. If you make it worse, you are messing with my air, exerting force on it. There is an amount of environmental degradation that comes with being alive. We breathe, we make trash, we mine elements to make things. The U.S. is by far the biggest part of that problem, and is doing little to nothing about it.