Multi-faceted Studies on Highly Oxidized Organic Molecules MUSHROOM

"Highly oxidized organic molecules (HOMs) are a key set of compounds in the atmosphere that have attracted considerable recent attention.1 The low volatility of these compounds means that they have an important role in aerosol formation and growth with a consequent impact on air quality and climate.
HOMs can be formed from simple organic species by a process known as auto-oxidation. For butane this could consist of the following chemistry. The initial radical formed (R), reacts with oxygen to give CH3CH2CH2CH2O2 (RO2). Now there is a competition between bimolecular reactions of RO2 with a range of atmospheric species (e.g. NO, NO2, HO2, RO2) and an internal abstraction to give a hydroperoxy radical CH3CHCH2CH2OOH. This process can then be repeated (addition of O2 to the carbon centre radical and internal abstraction) gradually introducing more functionality into the molecule and reducing the volatility.
The proposers are well-placed to study this chemistry. The mechanism of auto-oxidation was developed within combustion chemistry and Seakins has studied such chemistry in dimethylether combustion, and brings expertise in laboratory kinetics of combustion and atmospheric chemistry.2-3 This component of the project will look at individual or small groups of elementary reactions. All three proposers are involved in the operation of the Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC) which is another approach to obtaining kinetic information but with a complementary focus on the whole system rather than individual reactions. Heard is the PI on a NERC proposal looking at RO2 chemistry and Stone and Heard have particular expertise in monitoring RO2 species.4-5
The main focus of the project will be laboratory studies of gas phase species, but there will be scope to gain additional experience in modelling, calculations, fieldwork and aerosol chemistry depending on the interests of the student and how the project develops.

1. Bianchi, F.; Kurten, T.; Riva, M.; Mohr, C.; Rissanen, M. P.; Roldin, P.; Berndt, T.; Crounse, J. D.; Wennberg, P. O.; Mentel, T. F.; Wildt, J.; Junninen, H.; Jokinen, T.; Kulmala, M.; Worsnop, D. R.; Thornton, J. A.; Donahue, N.; Kjaergaard, H. G.; Ehn, M., Highly oxygenated organic molecules (hom) from gas-phase autoxidation involving peroxy radicals: A key contributor to atmospheric aerosol. Chem. Rev. 2019, 119 (6), 3472-3509.
2. Eskola, A. J.; Carr, S. A.; Shannon, R. J.; Wang, B.; Blitz, M. A.; Pilling, M. J.; Seakins, P. W.; Robertson, S. H., Analysis of the kinetics and yields of OH radical production from the CH3OCH2 + O2 reaction in the temperature range 195-650 K: An experimental and computational study. J. Phys. Chem. A 2014, 118 (34), 6773-6788.
3. Glowacki, D. R.; Lockhart, J.; Blitz, M. A.; Klippenstein, S. J.; Pilling, M. J.; Robertson, S. H.; Seakins, P. W., Interception of excited vibrational quantum states by O2 in atmospheric association reactions. Science 2012, 337 (6098), 1066-1069.
4. Onel, L.; Brennan, A.; Seakins, P. W.; Whalley, L.; Heard, D. E., A new method for atmospheric detection of the CH3O2 radical. Atmos. Meas. Tech. 2017, 10 (10), 3985-4000.
5. Mir, Z. S.; Lewis, T. R.; Onel, L.; Blitz, M. A.; Seakins, P. W.; Stone, D., CH2OO criegee intermediate UV absorption cross-sections and kinetics of CH2OO + CH2OO and CH2OO + i as a function of pressure. PCCP 2020, 22 (17), 9448-9459.

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