Ethylene Oxide and VOC Measurements Using a Cavity Ring-Down Spectrometer (CRDS)

Ethylene Oxide (EtO) is a hazardous air pollutant (HAP) used in the large-scale production of chemicals, as a sterilizing agent for medical devices, as a fumigant in certain agricultural products, and can be found in the atmosphere emitted from natural gas, cigarette smoke and diesel exhaust. While its carcinogenic properties have been known since the 1940s, the regulatory landscape around its emission and toxicity has evolved in recent years. Various studies and measurement campaigns are underway to better understand its sources and associated emission rates, and ultimately assess the risk to humans and the environment. We present a summary of methods that have been used to measure and monitor EtO using laser-based spectrometers based upon Cavity Ring-down Spectroscopy (CRDS). We begin with a summary of in-house testing of source and ambient EtO analyzers that can resolve ppt changes in EtO with a measurement interval of seconds. We present datasets from field deployments of the source analyzer in stack testing, continuous emission monitoring (CEM), and leak detection and repair (LDAR) applications. Though the initial focus was on characterizing EtO emissions at the source, we also present data from field deployments of our ambient analyzer and a novel method to reach a limit of detection in the low ppt range. CRDS-based systems provide significant advantages over legacy methods (GC, FTIR) in sensitivity, speed of response, simplicity, stability, and portability, as has been demonstrated in the last decade for the quantification of simple molecules like carbon dioxide, methane, or ammonia. Though our initial work has focused on measurements of specific hazardous air pollutants like EtO, there is future potential for speciated detection of other volatile organic compounds (VOCs) such at BTEX.