Controlling Air Pressure

Yes, an SMC ITV will turn voltage directly into pressure. They're not cheap - even at eBay prices they usually go for more than $200. They are 'industrial' which means they take a 0-10v input, necessitating a few components to interface to an Arduino.

Look into VSO valves for something that can be directly controlled by PWM - it turns voltage into flow - this will work for option 2.