Researchers could then determine whether hydrogen gas mixes with residual gas or oil, reacts with minerals in the surrounding rock or poses any environmental concerns. (sciencedaily.com)
I suppose the air could be cooler or have less exhaust gas mixed in it. (greencarcongress.com)
First, greenhouse gases mix globally in the atmosphere, and so damages are spread around the world, regardless of where the gases were emitted. (pathsoflight.us)