Use Cavorite
<PERSON> The First Men in the Moon introduces a reclusive physicist by the name of <PERSON>, who is working to develop an alloy that can shield against the effects of gravity. He successfully creates the material, dubbed Cavorite. In an early part of the story, a sheet of Cavorite is processed prematurely, and it causes the column of air above it to become weightless; which causes a powerful updraft as the non-weightless air applies enormous pressure on the column; the Cavorite, also weightless, hence shoots itself into space. The main characters are able to devise a system of windows that can negate the shielding that Cavorite applies, which enables them to make a steerable ship.
Cavorite is also featured as a plot point in <PERSON> graphic novel League of Extraordinary Gentlemen, where it is used to create an aerial warship which is unleashed in the climax of Volume I. In it, only a small amount of Cavorite can be used as the power source of an "engine" that provides lift for the enormous ship.
I highly recommend giving League of Extraordinary Gentlemen a look for the aesthetics alone; its setting is that of an enormously amplified Victorian era where late-19th and early-20th century contemporary speculative fiction is real. The movie, on the other hand, is bad and has nothing to do with the comic.
When Cavorite is used without a way to control the shielding, it causes air to escape the Earth's atmosphere. If you had a large enough sheet of it secured to the ground, then given enough time the Earth would be rendered airless and hence lifeless (or not, more on that later). 300
Furthermore, the force applied by atmospheric pressure on the now-weightless air has the potential to be destructive on its own. Ground-based Cavorite installations could, in theory, be used as a form of weather control, as the Cavorite effectively creates a persistent point of low barometric pressure.
All of this has a very relevant side-effect: Cavorite can be easily weaponized, but it is also controllable. Cavorite can only be manufactured through a specific process, and any country that wants to make large amounts of it would need to trade for some very specific machinery and materials. Due to this, we have a situation similar to Uranium, as another answer mentioned.
While mass quantities of Cavorite could be used in things like weather control, or power generation or what have you, the consensus is that it's simply too unsafe. This could be explored in a Chernobyl-like accident where a Cavorite power plant's shielding failed, which effectively created a permanent hurricane around the region that made it impossible to re-shield. The storm may rage to this very day. For this reason, it is simply not allowed to have Cavorite present in large concentrations anywhere.
While Cavorite could have many more uses if used in greater quantities, nobody's been foolhardy enough to try it yet; smaller quantities of Cavorite are only really useful in powering airships, so that's what the majority of it is used for.
In actuality, the air that is shot out from the Earth's atmosphere would dissipate, and it almost certainly would not have enough speed to escape Earth's gravity altogether, meaning virtually all of the air that gets ejected from the atmosphere would fall back to Earth. But of course, dissipation theory is still in its infancy so it's still widely believed that the accident at the Cavorite power plant could eventually suck all of the air out of the Earth. 435