Last time my wife and I went to Yellowstone in the winter, we ended up with a private tour in an old bombardier. It wasn't supposed to be a private tour, but we went so early in the winter season, just days after the park re-opened, that there was hardly anyone taking tours. So it turned out to just be the two of us. It was absolutely splendid, the park was gorgeous as usual, and everything was fresh snowfall.
We loved that tour, but there was one rather sad story our guide told us. Before the more recent, stricter rules on snowmobiles went into effect, people would take whatever cheap snowmobile they could get their hands on into the park. Of course, the cheaper the bike, the cheaper the engine, which meant most all the snowmobiles used very inefficient, and very dirty two stroke engines. Just imagine the exhaust from a gas powered lawn mower or chainsaw, magnified several times.
In winter, there's a phenomenon called an atmospheric inversion caused by the cooler air of the season. The inversion stops all vertical movement of the air, so exhaust from snowmobiles, instead of dissipating, collects and lingers near the ground.
Our tour guide is telling us this because during the peak of the winter seasons in the park, the rangers manning the entrances would often complain about the air quality. The entrances were particularly problematic because so many vehicles would be stopped there waiting to get into the park. Any time an inversion hit, all those fumes would get trapped.
Nothing was ever done about this until, one day, a park ranger passed out and died. He was a friend of our tour guide. This finally pushed them to add an air quality measurement station to the park entrance. Not too long after that, they started cracking down on snowmobiles.
Nowadays, only low-emission and low-noise snowmobiles are allowed into the park.
I have no idea if the story is true or not. But it's sad to think a park ranger had to die for such an obvious problem to get solved.
There are other sad stories about how we've managed Yellowstone. But it's a beautiful park, and it makes me so happy that, even if we goof sometimes, at least we are smart enough to put that land aside for generations to enjoy.