2.2.1. Microwave Irradiation
Metal nose clips of respirators were eliminated, and the respirators were exposed to microwave irradiation with 750 W power (MR-280M, LG Electronics, Seoul, Korea); for 1 min, the outer side was directed to the irradiation, then, for 1 min, the inner side was directed to the irradiation. All treated samples were stored for 12 h under ambient temperature before the filtration test.