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Open Path Spectroscopic Detection of Hydroxyl Radical: A Comparison between Broadband Cavity-Enhanced Absorption
Callum E Flowerday1, Ryan Thalman2, Matthew C Asplund1
1Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States.
Analytical Chemistry
|May 29, 2025
Summary
Measuring atmospheric hydroxyl radical (OH) is difficult. This study introduces broadband cavity-enhanced absorption spectroscopy (BBCEAS) instruments, offering improved field measurement capabilities for OH.
Area of Science:
- Atmospheric Chemistry
- Spectroscopy
- Environmental Monitoring
Background:
- Hydroxyl radical (OH) is the primary atmospheric oxidant, crucial for air quality and climate.
- Measuring OH is challenging due to its low concentration and short atmospheric lifetime.
- Existing field measurement techniques like LIF-FAGE and CIMS have limitations.
Purpose of the Study:
- To evaluate the performance of two novel broadband cavity-enhanced absorption spectroscopy (BBCEAS) instruments for measuring atmospheric OH.
- To compare BBCEAS with existing field measurement techniques.
- To assess the impact of aerosols and turbulence on BBCEAS performance.
Main Methods:
- Utilized two BBCEAS instruments: one with a CCD detector and another with a Fabry-Pérot interferometer (BBCEAS-FP).
- Employed an open-path configuration with a low-loss optic to measure cavity reflectivity.
- Used a butane flame as a controlled OH source for testing and calibration.
Main Results:
- The BBCEAS instrument achieved an extrapolated 1-h detection limit of 1.5 × 107 molecules/cm3.
- Applying a Gauss-Hermite filter improved the detection limit to 4.6 × 106 molecules/cm3.
- The BBCEAS-FP demonstrated a comparable detection limit of 1.5 × 107 molecules/cm3, offering a more cost-effective and portable solution.
Conclusions:
- BBCEAS instruments show promise for accurate and specific atmospheric OH field measurements.
- The BBCEAS-FP presents a viable, more accessible alternative for OH monitoring.
- Further research should investigate real-world performance under diverse atmospheric conditions.
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