Grantee Research Project Results
Final Report: Ethylene-oxide monitor with ultra-low limit of detection
EPA Contract Number: 68HERC21C0047Title: Ethylene-oxide monitor with ultra-low limit of detection
Investigators: Herndon, Scott
Small Business: Aerodyne Research Inc.
EPA Contact: Richards, April
Phase: II
Project Period: April 1, 2021 through March 31, 2023 (Extended to July 31, 2023)
RFA: Small Business Innovation Research (SBIR) - Phase II (2021) Recipients Lists
Research Category: SBIR - Air Monitoring and Remote Sensing , Small Business Innovation Research (SBIR)
Description:
Recently lowered exposure limits for ethylene oxide (EtO) in ambient air to 11 parts per trillion (long-term, 10E- 4 risk level) will require advanced technology. We have developed such technology in this project.
We have developed and improved an ethylene oxide (EtO) monitor based on laser spectroscopic detection that quantifies EtO in real time with high precision. We have tested this instrument in the laboratory and in real-world field campaigns.
Summary/Accomplishments (Outputs/Outcomes):
Improve Overall Performance and Usability of the Instrument
The core of this SBIR aimed to enhance the technical performance and the commercial potential of the Ethylene Oxide (EtO) Dual-TILDAS system. Using a novel method for super-cell alignment, the instrument was configured to trace a 413 m pattern in the Aerodyne Astigmatic Mulitpass Absorption Cell (AMAC). The upgraded instrument achieved nearly a four-fold increase in performance compared to the previous cell. By the conclusion of the project, we have achieved a 1-sigma 50 part-per-trillion (ppt) precision in 1 second and, using a refined zeroing strategy, achieves a precision of 3.6 ppt in 1 hour averaging time (Figure 2).
Figure 1. Time series (a, b) and Allan–Werle variance plots (c) showing EtO precisions at various averaging times while stationary with 2 min autobackgrounds (blue) and while mobile on the high- way with 10 min backgrounds (red). The stationary data (a) average to 32.6 ppt EtO with a 1 h smooth (dotted line) shown. Figure from Yacovitch et al. 2023
Zeroing Options
Our focus on zeroing strategies aimed to improve the accuracy of EtO measurements at background sites. We explored two zeroing methods: dry and humid. The dry method used ultra zero air (UZA), an EtO-free, dry air source. Despite facilitating precise long- term averages, it occasionally resulted erroneous negative average EtO mixing ratios due to imperfection in the representations of line-shape wings when the sample was humid ambient air.
The "humid zeroing" method aims to match humidity during the zeroes. This approach successfully quantified ambient EtO concentrations without yielding significant negative averages.
We tested several different scrubber materials in pursuit of humidity-matched zeroing, and have identified a catalytic scrubber which, when held at moderately elevated temperatures, selectively destroys EtO. We have characterized EtO breakthrough for this scrubber at extreme EtO concentrations to be between 0.5% and 1.1% at 150C (breakthrough defined as EtO concentration after the scrubber divided by the concentration without the scrubber). Catalytic scrubbing provides two main benefits: it allows for instrument auto backgrounding and zeroing without the need for consumables and offered a humidity-matched zero.
Spectroscopic Accountability and Interferers
The spectrometer operates at low pressure and can fully resolve EtO's features present in the chosen absorption band. TILDAS can fit multiple species to the Beer's Law model. Species that absorb in this wavelength region have unique fingerprint features of their own and when they are included in the fit model, the influence of the interferent can be mitigated. Methanol is one such interferer, particularly during vehicle cold starts. We also detected unknown substances, hinting at potential exhaust interferers.
A key challenge we faced was to identify and handle those potential interferers that might affect EtO quantification. We found that high concentrations of species in excess of ~20 ppm methane enhancements and ~200 ppb ethene often resulted in negative EtO concentrations. This was further compounded by software limitations, which restricted the number of species that could be fit in the EtO region to six, including EtO, CH4, C2H6, C2H4, H2O, and HCHO. Ozone, which is not typically an issue for EtO measurement, was found to cause observable interferences only at ppm levels.
We also measured the headspace of several common vehicle fluids such as Antifreeze, DEF, and Windshield Washer Fluid as interferers. Antifreeze was found to increase water concentration and formaldehyde. DEF contains distilled water and urea but also gave off a moderate signal of methanol. Windshield washer fluid primarily contains methanol, and other compounds like ethanol, ethylene glycol, or propylene glycol. Methanol caused significant signal in the EtO-TILDAS.
Aerodyne's instrument saves each of the spectra it collects. Simple examination of the spectra during noteworthy plume encounters enables users of the technology to report results with confidence and accountability.
Demonstrate Accuracy without Calibration
Our ability to demonstrate accuracy without calibration marks a significant milestone in our project. Our initial attempts at calibration displayed poor reproducibility, with calibration factors deviating by as much as 30%. To address this, we developed a new calibration procedure, which significantly improved reproducibility and reduced the deviation to 3%.
During the South Coast Air Quality Management District (SCAQMD) EtO study, we conducted several calibration experiments using two calibration tanks. The calibration factors were determined using a mix of dry dilution calibrations and humid standard addition calibrations. The robustness of our calibration procedures was further confirmed by comparing the results of the TILDAS-FD-EtO instrument with those of a gas chromatograph with an electron ionization time of flight mass spectrometer (GC-EI-ToF). The calibration procedure remained robust, and the TILDAS-FD-EtO line intensities remained traceable to EPA-approved standards, underscoring the accuracy of the calibration process.
Alternate Spectral Region at 870 cm-1
Our team sought to minimize spectral interferences by exploring an alternate spectral region at 870 cm-1. This new region, less crowded with other hydrocarbon absorbers, would have enabled ethylene oxide detection with fewer interferences. We commissioned a new laser from a laser manufacturer to operate in the 870 cm-1 region, but it failed, as did a second replacement device. Currently, we are working with this manufacturer to understand and solve the issue. The move to this new spectral region will unlock new avenues investigations but will have to be done in the future when we can get a reliable device.
Field Demonstrations
Our project reached critical milestones with a series of field demonstrations, successfully showcasing our EtO-TILDAS technology in various field conditions. These campaigns allowed us to examine numerous potential EtO sources and their respective emission levels, further emphasizing the value and potential of our technology.
The instrument has been deployed on 6 separate field projects in several regions, including projects aimed at measuring industrial emitters of VOCs and other toxics. This instrument exhibited excellent interferer-free performance. Two campaigns involved collaborators using competitor technology; the EtO-TILDAS demonstrated superior interference-free operation hydrocarbon-rich environments, surpassing the performance of the Picarro EtO analyzer.
During these campaigns, we assessed numerous potential EtO sources, primarily commercial sterilization companies. Every commercial sterilization facility visited displayed some level of EtO emission detectable at their fenceline, with peak concentrations varying from 1-2 ppb to hundreds of ppb (Figure 1). Many have since faced regulatory scrutiny and implemented emission reductions in response to our measurements.
Conversely, no EtO enhancements were detected at hospitals (including those known to use EtO), nor at food product warehouses where EtO could reportedly be used for sterilizing spices and other powdered products. We hypothesize that hospitals use EtO intermittently, in small amounts, and with exhaust treatment.
With these field demonstrations, we have validated the effectiveness and reliability of our EtO-TILDAS technology under various conditions and environments, underscoring its potential for wide-ranging applications.
Figure 2. Summary of transects downwind of Facility A (a commercial sterilization facility). Transects are plotted normal to the wind vector for paths driven along 3 roads approximately 35 m (a), 600 m (b) and 1.4 km (c) downwind of Facility A. The average of 600 m transects (black dotted line) is shown for Panel B. A map (d) shows the facility location (red square) with the three main transect roads labelled by distance downwind. The driven path is colored and sized by EtO concentration. Wind barbs (blue) are tethered to the truck path, with feather end of the staff pointing into the wind. Figure from Yacovitch et al. [2023]
Conclusions:
We have demonstrated that we can measure EtO in ambient air without sample preparation or preconcentration with a 1-sigma precision of 50 ppt (parts per trillion) in 1-second. We have shown that with further data averaging we can improve the precision to 3.6 ppt in 1 hour.
This is a truly remarkable result and places our technology far ahead of any other existing technology. We have demonstrated this technology in several real-world field campaigns.
The research and development activities under this project have been extremely successful. While a portion of the field demonstration work was conducted for its intrinsic scientific value, the overall goal has always been to use these tasks and demonstrations to generate a better commercial product and serve the ethylene oxide monitoring market.
The market is described by two sectors: Air Quality Monitoring and Industrial Operators. The versatility of the technology developed in this project has led to three models of ethylene oxide instruments: high sensitivity ambient, fenceline monitor, process gas monitor. Over the course of this project, we have issued a total of 7 quotes that are pending, with 1 confirmed sale as of this draft.
The laser group at Aerodyne has marketed the ethylene oxide spectrometers through featured stories on our website and at scientific conferences and the National Air Quality Conference.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 2 publications | 2 publications in selected types | All 2 journal articles |
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Type | Citation | ||
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Galarneau, E., T. I. Yacovitch, B. Lerner, A. Sheppard, B.-T. Quach, W. Kuang, H. Rai, R. Staebler, C. Mihele, and F. Vogel (2023), From hotspots to background:High-resolution mapping of ethylene oxide in urban air, Atmos. Environ., 119828, doi:https://doi.org/10.1016/j.atmosenv.2023.119828. |
68HERC21C0047 (Final) |
not available |
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Yacovitch, T. I., C. Dyroff, J. R. Roscioli, C. Daube, J. B. McManus, and S. C. Herndon (2023), Ethylene oxide monitor with part-per-trillion precision for in situ measurements, Atmos. Meas. Tech., 16(7), 1915-1921, doi:10.5194/amt-16-1915-2023. |
68HERC21C0047 (Final) |
not available |
SBIR Phase I:
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.