[D13]

As noted above, it is the vacuum actuator for the heat riser. When the engine is cold, it uses exhaust heat to help the engine warm quicker, improving cold driveability and yes, reducing cold emissions. The tubing is part of the vacuum control system that goes to a Thermal Vacuum Switch (TVS) that looks at the engine temp to turn the actuator on or off. One line vacuum to the switch, the others are to devices to be turned on or off.
If you do remove the actuator make sure to wire the valve in the open position.