Methodology

Various laboratory and computational tools are used in the atmospheric chemistry group for quantitative studies of chemical reactions. The laboratory measurements at UoN are performed in a flow cell apparatus which couples gas flow with a photolysis laser and probe radiations. Reactive intermediates are probed in real time, under various chemical and physical conditions simulating the troposphere, using spectroscopic methods such as Cavity Ring-Down Spectroscopy (CRDS).

CRDS involves using an optical cavity made of highly reflective mirrors in which probe laser radiation is ‘trapped’ to increase interaction time between the radiation and gas sample. This effectively results in long absorption pathlength and enhanced detection sensitivity suitable for radical spectroscopy. With CRDS, we measure kinetic and spectroscopic parameters such as rate coefficients, product yields and absorption cross-sections which can be directly used in the chemical models of the atmosphere.

References:
Chhantyal-Pun et al. J. Phys. Chem. Lett. 2010, 1, 1846-1852
Chhantyal-Pun et al. Phys. Chem. Chem. Phys. 2015, 17, 3617-3626

We also collaborate with Drs Wahid Mellouki and Max McGillen at ICARE-CNRS in Orleans, France, to use the outdoor atmospheric simulation chamber facility, HELIOS, for characterizating Criegee intermediate chemistry during ozonolysis of alkenes. Simulation chambers provide a controlled environment for measuring chemical processes under realisitc atmospheric conditions. We make use of novel scavengers to ‘trap’ Criegee intermediates into adducts and detect them using either NH₄⁺ or H₃O⁺ proton transfer reaction mass spectrometry.

Quantum chemistry calculations are used by the group to characterize reaction pathways, radical spectroscopy and ionization efficiences which provide physical insights into our laboratory measurements. Numerical modelling approaches are used to analyse kinetic data from our laboratory measurements and to estimate their atmospheric implications.

References:
Ren et al. Faraday Discuss. 2017, 200, 289-311
Chhantyal-Pun et al. ACS Earth Space Chem. 2018, 2, 833-842
Chhantyal-Pun et al. ACS Earth Space Chem. 2020, 4, 1743-1755