The atmosphere consists of a vast pool of trace gases, which are present at levels less than 1 ppmv of air and some even lower than that. The effect of these trace species on the atmosphere is disproportionate to their abundances. They are responsible for various phenomenon ranging from urban photochemical smog, acid deposition, ozone depletion and formation in stratosphere and troposphere respectively, to potential climate change. In this regard, the high reactivity of trace species like, radicals make them the most relevant species in the Earths atmosphere as they react with most of the pollutants those are released into the atmosphere, majorly by man-made activities. Those pollutants are constituted mostly by polycyclic aromatic hydrocarbons (PAHs) and ultimately forms various secondary organic aerosols (SOAs) when oxidation products of the volatile organic compounds (VOCs) deposit onto existing particles or form new particles. These SOAs accounts for a major fraction of the global atmospheric sources of aerosols that are considered to be highly detrimental to both the environment and human health. The lifetime of these atmospheric trace species depends upon how fast they react with the oxidants in the Earths atmosphere. Thus, the kinetic investigations involving atmospherically relevant radicals is essential to gauge the environmental impact of anthropogenic activities and helps us in mitigating the global menace of air pollution and its subsequent impacts.
In recent years, Cavity Ring-Down Spectroscopy (CRDS) has evolved as a viable tool for trace gas sensing and investigate the kinetics of these species, as the limitation of sensitivity of conventional absorption spectroscopy is avoided by using an effective pathlength of kilometers with the help of an optical cavity made by two highly reflective mirrors. Using the laser-based CRDS technique, the radicals are produced in-situ and their absorption spectrum as well as their absolute kinetics can be investigated with high accuracy. The gas phase kinetics of peroxy radicals [1], C-based aromatic radicals [2], iodine oxide radicals [3] and Criegee intermediates [4] with various molecules of atmospheric interest, will be discussed in the seminar.
References:
1. Rolletter, M.; Assaf, E. Assali, M.; Fuchs, H.; Fittschen, C. J. Quant. Spectrosc. Radiat. Transfer 2020, 245, 106877.
2. Minamida, M.; Tanaka, K.; Tonokura, K. Int. J. Chem. Kinet. 2020, 52(2), 77-83.
3. Foreman, E.S.; Murray, C. J. Phys. Chem. A 2015, 119(34), 8981-8990.
4. Chhantyal-Pun, R.; Khan, M.A.H.; Martin, R.; Zachhuber, N.; Buras, Z.J.; Percival, C.J.; Shallcross, D.E.; Orr-Ewing, A.J. ACS Earth and Space Chem. 2019, 3(10), 2363-2371.