I just had an idea – likely an absurd one – but it could make an interesting plot.
Picture this scenario – Present day earth. (easy to picture) But, there is an antagonist. He has a facility full of powerful air compressors and vacuum pumps. He also has lots of massive (heavily armored) air tanks, to store the air. He then begins depleting the atmosphere. He threatens all major world governments (and anyone with enough money to be worth it) that he will completely deplete the atmosphere and kill all life on earth unless an absurdly high ransom is met. If it is met, he will release the air again, replenishing the atmosphere.
However, the protagonist organizes a team, infiltrates the facility, damages the already highly pressurized containment tanks, and plants explosives near the damaged parts. They escape far enough away, and detonate the charges. The tanks explode violently, releasing all the air back into the atmosphere.
For um... reasons the various world powers can't just attack the facility directly.
The atmosphere obviously contains an absurd amount of gas - it is really, really huge. The antagonist only needs to deplete a small portion of the atmosphere - just enough so there is a difference in its density noticeable enough to scientists so that the antagonist's threat of total depletion seems valid.
My question is, how (without hand waving) is it remotely possible for the atmosphere to be even partially depleted, pressurized, and then contained on any number of containment systems on the earth's surface? Specifically, how big of a storage system would be needed to make a noticeable difference in the atmosphere's density? (assume you can use any material currently known to make the air cylinders - no unubtanium bottles that can hold a few trillion PSI.)