switching air valve with Arduino Micro
Use this circuit to control a solenoid valve:


You can use AO3400A as  N-channel MOSFET, if you are OK with SOT-23 package. Or use IRLZ44N, which is many times more than enough for your load.

Make sure you use flywheel diode D1, it is to protect MOSFET. I think 1N4148 would be enough.

Connect Arduino's ground (negative of voltage source) with the GND shown in circuit.