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Monitoring and Mitigating Ethylene Oxide Emissions: Montrose Environmental’s Innovative Solutions

Ethylene oxide (EtO) is a highly versatile compound used extensively in various industries including medical device manufacturing, sterilization processes, and chemical production. It is a critical component that is very important in many applications. However, its potential adverse effects on human health and the environment have raised concerns among regulatory bodies and communities residing near industrial facilities that utilize EtO.

Starting in early 2019, many facilities began proactively preparing for the looming EtO updates presented by the U.S. Environmental Protection Agency (EPA). Now an updated standard for EtO seems inevitable for issuance in 2024. With the update comes stricter testing and monitoring regulations for EtO throughout the industry as well as an updated Performance Specification (PS-19) specifically developed for facilities where a Continuous Emissions Monitoring System (CEMS) is required. Several questions remain, but one of the main points of contention is, “With emission limits for EtO being so low, which technology works best for my current application?”


Montrose was tasked with addressing these testing and detection limit concerns related to EtO at several different sampling locations throughout multiple facilities. Facilities were predominantly interested in ambient, fenceline, and CEMS-based applications to determine what technologies were being offered and what seemed to work well. A bench-top study only goes so far as to prove actual results found in the field so we wanted to put a few pieces of promising technology head to head and determine what fits best. 

After countless tests, research, and development, we found a technology that delivers on detection limits, data quality, and real-time measurements. Luckily this instrumentation was already an approved tool under EPA Method 320 and meets the strict and evolving PS-19 requirements thus making our decision to move forward even easier.

Montrose then needed to install and test this system to ensure compliance and guarantee that the system was online and reliable well ahead of the 2024 deadline. Montrose was able to collaborate with the industry-leading instrument manufacturer Thermo Fisher Scientific to provide a solution for the industry. The system needed to meet strict performance standards, obtain parts per billion (ppb) detection limits for EtO, and provide data continuously for coverage 24 hours a day 7 days a week. Lastly, the system needed to pass a relative accuracy testing audit (RATA) to finalize the commissioning of the system. 


Montrose Environmental deployed real-time EtO EMS-10 Continuous Emissions Monitoring Systems, manufactured by Thermo Fisher Scientific, to track EtO emissions accurately and precisely at several facilities nationwide. These systems enable continuous monitoring and data collection to assess the concentration levels of EtO in a wide array of environments and facility processes. Furthermore, these systems were able to provide EtO detection limits in the single-digit ppb range on processes that have variable stack concentrations and conditions. By deploying innovative monitoring equipment, Montrose could ensure timely and accurate detection of EtO concentrations, allowing for process understanding, ensuring compliance, and informing sites of immediate corrective actions if necessary. 

Once installed, as these are permanent CEMS systems, they are required to undergo yearly relative accuracy testing audits (RATAs) which are generally done by third-party stack testing vendors. Montrose’s Stack division began RATA testing these systems in 2023 and data has shown that these systems are consistent and reliable for facilities that utilize, store, or produce EtO. The preferred technology for these RATA programs is an optically enhanced Fourier-transform infrared spectrometer (OE-FTIR) as it is a versatile piece of equipment. It is widely used and accepted in the industry, meets upcoming PS-19 requirements, and better yet is already an approved EPA method for testing (Method 320). Last but not least, it can handle variable stack concentrations which has been shown to be challenging for other existing EtO technologies which are designed for ambient air monitoring.


Montrose’s commitment to addressing EtO emissions has yielded positive results. The implementation of advanced monitoring systems has allowed for the accurate measurement of EtO levels in chemical plants, sterilization facilities, and more. Many sites and sources including ambient, fence-line, post-abatement, and more are able to achieve one ppb of EtO detection or less. 

The EMS-10 Continuous Emissions Monitoring Systems continue to monitor 24/7 and yearly RATA tests have proven to be successful in verifying that both the equipment and facilities are within compliance. These tests have also been submitted to the EPA and state agencies for quality assurance. As the new Performance Specification (PS-19) continues to develop and evolve for EtO, the OE-FTIR technologies provided by Thermo Fisher Scientific will continue to provide reliable results, meet all of PS-19 criteria, achieve ultra-low detection limits, and are well ahead of the curve for implementation.

Our Solution

Montrose Environmental Group’s focus on monitoring and reducing ethylene oxide emissions demonstrates its commitment to environmental responsibility, worker safety, and industry understanding. By implementing real-time monitoring systems and collaborating with industry leaders, like Thermo Fisher Scientific, Montrose provides effective solutions to address the challenges posed by EtO emissions.

Through our efforts, Montrose Environmental Group contributes to a safer work environment and healthier communities. Our dedication to monitoring ethylene oxide emissions sets a benchmark for other organizations, encouraging them to adopt proactive measures to protect public health and ensure regulatory compliance.

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