Liquid aerators are a chemical solution that is mixed with water and sprayed onto a lawn. The solution is absorbed into the topsoil and mixed with the dirt. The liquid is designed to expand after contact with open air and push the soil apart. After expansion, the liquid evaporates, leaving gaps filled with air in the soil and breaking up compacted areas.
Gas powered aerators have wheels and a set of hollow spikes that stick out from a central core. As the aerator is pushed across the lawn like a lawnmower, the engine turns the core and sinks its spikes into the ground, pulling out plugs of soil in an even spread.
Hand aerators are poles with tines at the bottom and a handle at the top. They are designed to do small areas other aerators can't reach by being manually driven into the ground repeatedly to break up the soil.
Towed aerators are made of a central drum from which tines protrude at regular intervals. They are attached to a tractor's hitch and roll behind the tractor as it is driven around the entire lawn. The weight of the drum provides enough force to drive its tines into the ground to break it up.