Kinetic Isotope Effects in Atmospheric Sinks of Methane (CH4)
The current understanding of methane kinetic isotope effects (KIEs) in reactions with atmospheric oxidants, such as the hydroxyl (OH) radical and chlorine (Cl) atom, is a limiting factor in the precise determination of the methane budget from atmospheric δ13C and δD measurements. Several recent studies have highlighted this and suggested new laboratory measurements to improve the current uncertainty in methane KIEs. Recently, we received a research grant from the National Science Foundation’s Division of Atmospheric and Geospace Sciences (NSF-AGS) to work in this area. We are in the process of fabricating a state-of-the-art temperature and pressure-controlled laser photochemical reactor, coupled with online and offline spectroscopic instruments, for monitoring relevant chemical species inside the reactor. The online instrumentation includes an FTIR spectrometer, as well as a UV absorption setup with a Pen-ray lamp light source and a photodiode detector. Tunable Infrared Laser Direct Absorption Spectroscopy (TILDAS) is employed offline for high-precision measurement of methane isotopologues (δ13C and δD). We plan to cover a wide temperature range, relevant to the entire troposphere and beyond, which has not been done before for 13CKIEOH measurements. Extensive variation in our experimental conditions and process-free gas analysis is expected to yield bias-free, high-precision KIE measurements. The improved uncertainty in our measured KIEs is expected to better constrain the global CH4 budget from atmospheric CH4 isotopic measurements.
This project is being supported by NSF Award AGS - 2516797