Well, I', mot a mechanic but it looks like I'm the best you'll get. First,you are talking about two different types of braking systems. The "service brake" for driving, which is hydraulic and according to your decsription should have a little air added. JUST KIDDING!!! It is either just fine or adjusted a little tight.
The parking, or emergency brake is not hydraulic and therefore would not have any problem with air. Usually, it works by pulling a handle or stepping on a pedal with a ratchet that holds it . This pulls on a cable which underneath, about the middle of the car pulls on two cables, one going to each wheel. Where the one cable meets the two cables, usually there is a threaded rod which is where you would adjust the parking brake. If it only needs adjustment, that is where you would do it. Before you do that, look to see how much of the adjustment is already taken up. The cables may have stretched or frayed, or may have slipped out of guides which hold them away fromn the exhaust or frame. At the axle, they may slide inside a flexible metal hose which may have rusted and started to collapse, which increases the distance the cable has to pull in order to hold the brake. Finally, if the brake is not assembled or adjusted properly, you might get this as well. Inspect the entire system before you assume it only needs adjusting. It's pretty straightforward once you look at it. You want the brake adjusted where you start to feel resistance about one or two clicks, and should stop well before the end of it's travel.