The density of air is about 1.2 kilograms per cubic meter (water is 1000 kg/m3). So, it'd take about 830 cubic meters of air to make a ton (1 m x 1 m x 830), or a cube with each side of length 9.4 meters or about 30 feet.

A ton is a ton, regardless of phase (solid, liquid, gas, feathers)

The relationship between pressure, volume, and temperature for 1 ton of air (mass) can be characterized reasonably well by the ideal gas law PV=nRT

https://en.wikipedia.org/wiki/Ideal_gas_law

Weight a container in a vacuum chamber. Then put the air inside it, seal and weight it again. It's enough air that the full container weights a ton more than empty.

If you compress it, it keeps the same weight (to any reasonable precision), but you won't get it into a solid.