This is especially tough, because nobody likes to credit Nixon with anything, but the clean air act has really set the United States apart from almost every other country following the modern industrial era.
There are filters that factories in any country can put on their chimneys relatively cheaply to the profit of production, and in many other countries they do not, because they are not legally required to.
So yes, Nixon was a bigoted a******, but he did pass the clean air act, which directly lead to the fortified amendments to the clean water act a couple years later and significantly improved responsibility and maintenance of clean US environments (except for those allocated to native Americans, which are, to this day, horrifyingly abused so that native American waterways give native Americans cancers at obscene levels).
But generally, for most of you guys reading this, you can thank Nixon for the very clean air and water Americans take for granted.
We should also include the warmonger Teddy Roosevelt in that gratitude because he preserved so many natural landscapes.