Grantee Research Project Results
Final Report: Ethylene-Oxide Monitor With Ultra-Low Limit of Detection
EPA Contract Number: 68HERC20C0029Title: Ethylene-Oxide Monitor With Ultra-Low Limit of Detection
Investigators: Dyroff, Christoph
Small Business: Aerodyne Research Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2020 through August 31, 2020
Project Amount: $99,998
RFA: Small Business Innovation Research (SBIR) - Phase I (2020) RFA Text | Recipients Lists
Research Category: SBIR - Air and Climate
Description:
We are developing an ethylene-oxide (EtO) monitor with ultra-low limit of detection based on sensitive and selective optical measurement technology. The recent decrease of the exposure limits in ambient air to 11 parts per trillion (long-term, 10E-4 risk level) will require advanced technology to monitor EtO. Current methods require sample trapping and preconcentration to achieve an acceptable limit of detection (LoD), however the approach is susceptible to cross interference from other gaseous volatile organic carbon species. Our optical technology is direct, sensitive, and selective in the measurement of EtO without the need for sample collection, preconcentration, or any other sample preparation. The goals for the monitor are relative and absolute uncertainties of the 11 ppt exposure limit in less than 2 minutes. The system resulting from this research will enable both ambient air monitoring and industrial fenceline/facility detection of EtO. End users will primarily be state and federal EPA offices and other local and regional environmental agencies, as well as industrial EtO producers and consumers aiming to comply with regulations.
During Phase I, we targeted three goals to demonstrate the viability of this novel sensor:
(1) identify the ideal spectral region to probe EtO with the maximum precision and minimum cross interference. (2) develop a method for rapidly acquiring highly reliable background spectra and for demonstrating that this method delivers accuracy of ~10 ppt near the detection limit. (3) demonstrate measurements EtO with an accuracy of 5% (or 10 ppt below 200 ppt) without the need for frequent calibration with an EtO calibration standard, i.e. demonstrating a linear response of our prototype to changes in EtO.
Summary/Accomplishments (Outputs/Outcomes):
We have setup a prototype ethylene-oxide (EtO) monitor. This instrument uses laser spectroscopy and a long-pathlength sample cell to measure absorption spectra of EtO with high precision in real time.
We have selected a laser of suitable wavelength to detect EtO with the best compromise of sensitivity (precision) and selectivity. We have performed both experimental and theoretical work to identify gaseous species that absorb in our target wavelength region. We have included these species in our spectral fit to mitigate potential cross sensitivity.
To achieve best accuracy, our EtO monitor relies on frequent zero air measurements. These background measurements are designed to capture the time-dependent spectral baseline, i.e. a spectrum without absorbers. Typically, we would do this by measuring ultra-zero air from a compressed cylinder. In this project we want to avoid consumables to minimize maintenance of the monitor during deployment by customers. To this end we have identified materials that scrub EtO from ambient air to generate EtO free air for background measurements. Activated charcoal is an easy passive method to remove EtO (and other species) from ambient air. Filter cartridges would have to be changed from time to time, though. We also found that a Nafion dryer (typically used to remove water from air) is extremely effective in removing even parts per billion levels of EtO. The advantage in using a Nafion dryer is that it is entirely maintenance free.
We have demonstrated that we can measure EtO in ambient air without sample preparation or preconcentration with a precision of ~12 ppt (parts per trillion) for a 2 minute measurement. We have shown that with further data averaging we can improve the precision to better than 5 ppt for a 30 minute measurement. This is a truly remarkable result and places our technology far ahead of any other existing technology.
We have demonstrated that with background measurements every 2 to 3 minutes we are able to accurately measure zero EtO repeatably. This is important as this fact together with the high precision also informs us about our projected accuracy at low ambient EtO levels. The frequent background measurements effectively compensate for instrument drift. We have documented this using the Allan-Werle-variance method (a statistical method to quantify noise and instrument drift at different timescales). Using these results, we can reliably estimate the projected instrument performance in terms of precision and accuracy. For our instrument, drift at long timescales is very low due to the background measurements, and we expect accuracy below 10 ppt for measurements of 30 minutes or longer.
We have demonstrated the highly linear response of our EtO prototype instrument to changes in EtO concentration. To do so, we have set up an EtO delivery system based on dilution of a (nominally) 1 ppm (parts per million) EtO cylinder into a flow of zero air. These measurements were performed between zero EtO via a few tens of ppt up to ~ 4 ppb. We note that this was not a true calibration as the EtO cylinder was not certified. We will be performing true calibration tests during Phase II of this project. Our goal here was to demonstrate linear response, which is a weak point in other detection technologies, especially at low EtO concentrations. We have succeeded demonstrating linearity.
Conclusions:
The results we have achieved with our prototype EtO monitor during Phase I of this SBIR project are excellent. We have demonstrated our capability to detect EtO without preconcentration with very high precision of ~11 ppt in 2 minutes measurement time. We have further demonstrated that our technology offers linear response to EtO at parts per trillion levels of EtO because our technology is not only highly sensitive but also very selective. We are very confident to provide a complete EtO measurement package at the end of Phase II that will provide industry leading sensitivity and accuracy directly in ambient air.
We have been getting in touch with several potential customers that showed interest in our EtO measurement capabilities. These customers are of both the scientific air quality community as well as from larger chemical companies. With the former we are working on setting up technology demonstration field measurements. These measurements will provide an excellent opportunity to perform side-by-side intercomparisons with the existing EtO measurement techniques. The potential commercial customers are more interested in a final commercial product and we will keep in touch with them throughout Phase II.
SBIR Phase II:
Ethylene-oxide monitor with ultra-low limit of detection | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.