Time-resolved HO₂ detection with Faraday rotation spectroscopy in a photolysis reactor

Area of Science:

• Chemical Kinetics
• Spectroscopy
• Environmental Monitoring

Background:

• Radical species like HO2 are crucial in atmospheric chemistry and combustion processes.
• In situ monitoring of HO2 is challenging due to its high reactivity and low concentrations.
• Conventional methods like laser absorption spectroscopy (LAS) face limitations in dynamic environments.

Purpose of the Study:

• To present the system design and implementation of Faraday rotation spectroscopy (FRS) for radical sensing.
• To demonstrate high-sensitivity and time-resolved in situ detection of HO2 radicals.
• To compare the performance of FRS with conventional LAS in a photolysis reactor.

Main Methods:

• Utilized Faraday rotation spectroscopy (FRS) for Zeeman splitting detection.
• Implemented a digitally balanced acquisition scheme for enhanced sensitivity.
• Conducted experiments in a photolysis reactor to simulate dynamic environments.
• Compared FRS performance against laser absorption spectroscopy (LAS).

Main Results:

• Achieved high sensitivity (100 ppb) for in situ HO2 detection.
• Demonstrated successful HO2 detection using FRS where LAS was deficient.
• FRS showed favorable precision compared to LAS when applicable.
• Highlighted FRS immunity to spectral interferences like hydrocarbon absorption and optical fringing.

Conclusions:

• FRS is a highly sensitive and robust technique for in situ HO2 detection in dynamic environments.
• FRS offers significant advantages over LAS, particularly in complex chemical systems.
• The developed FRS system enables accurate radical monitoring, advancing chemical kinetics and atmospheric studies.