This white paper outlines testing performed using Picarro’s continuous emissions monitoring system (CEMS) on a LESNI EO Catalytic Abatement Plant (CAP). This testing was performed at a medical device manufacturer and sterilizer facility in the United States during an active sterilization process. Ethylene oxide (EtO, EO) concentrations were measured in real time upstream of the Catalytic Oxidizer (CatOx), and downstream, at the stack, to assess the destruction efficiency of the CatOx itself. Picarro’s CRDS monitoring systems capably and repeatably measured single and double-digit parts-per-billion (ppb) values of EtO at the stack and triple digit parts-per-million (ppm) values on the inlet, providing fast, sensitive data to demonstrate the superior destruction efficiency of the LESNI CatOx. The LESNI EO CAP kept concentrations at the stack below 100 ppb on an hourly-averaged basis, with a 24-hour average of just 12 ppb, and with an incredible average destruction efficiency of 99.991%, well above the 99.94% required for large facilities by the new US EPA National Emission Standards for Hazardous Air Pollutants (NESHAP).