Abstract: A load port assembly includes a stage for supporting a substrate storage pod, a port plate with an access port, and a gas curtain device mounted on the port plate for forming a gas curtain having a width sufficient for shielding the access port. The gas curtain device includes an elongated casing and a gate mechanism. A curtain-forming gas is discharged from an elongated port of the elongated casing to form the gas curtain. A gate mechanism is mounted to the elongated casing and is configured to be actutable so as to vary a thickness of the gas curtain. A purging method for the substrate storage pod on the load port assembly is also disclosed.