The Mysteries of Atmospheric Chemistry: Transient Absorption Spectroscopy Study Using FERGIE

background
Dr. Daniel Stone's research team from the University of Leeds in the UK is primarily focused on the study of oxidation reactions in the atmosphere and combustion processes. Dr. Stone is particularly interested in the chemical reaction processes of active substances that can control atmospheric composition and fuel combustion processes, such as hydroxide (OH), peroxide (HO2), and Crigee intermediates. In order to complete relevant testing and experiments, he not only needs to conduct research in the laboratory, but also needs to conduct field measurements and numerical simulations.

Figure 1: Absorption spectroscopy experimental equipment connected to the FERGIE system
challenge
Dr. Stone has conducted extensive research on the kinetics of the Krich intermediate (CH2OO) in the laboratory in the past. By using laser induced fluorescence spectroscopy to monitor the reaction products of HCHO, his work for the first time directly measured the CH2O reaction kinetics with pressure as a parameter (Stone et al., 2014). His work also indicates that under atmospheric conditions with the presence of oxygen, the photolysis of CH2I2 can lead to the production of a large amount of CH2OO (Stone et al., 2013). This conclusion has had a significant impact on understanding the oxidation process in coastal iodine rich areas.

Since then, Dr. Stone's research team has been dedicated to developing an infrared absorption experiment based on Quantum Cascade Laser (QCL) to directly monitor the amount of Kriging intermediates and SO3 generated during the reaction between Kriging intermediates and SO2 under atmospheric conditions. These experiments can evaluate the impact of sulfuric acid and sulfate aerosols produced by Kriging chemical processes on the atmosphere, and further explore their impact on air quality and climate change.

Dr. Daniel Stone: "Once FERGIE was integrated into the previous experimental setup, I was able to freely determine the triggering factors and obtain relevant time-dependent data within one measurement day."

Solution
Dr. Stone designed a clever experiment by first using high-power laser pulses to perform flash photolysis on gas mixtures, and then using the FERGIE system (predecessor of Isoplane81) to measure the instantaneous absorption of the gas mixture after photolysis. By connecting the fiber optic cable to the existing fiber optic port of FERGIE in the experiment, the trigger input of FERGIE can be synchronously collected with the external delay generator.

By utilizing FERGIE's spectral dynamics mode (with a window height of 50 rows), the time scale of each spectrum can be shortened to 290 microseconds. This reduces the time scale of the experiment by 5-6 times, expanding the spectral absorption research that could only be conducted on the millisecond scale to the sub millisecond scale. If the experiment is repeated 100 times, the sensitivity will also be improved.

Figure 2: FERGIE spectrometer product diagram

Source: Sohu