Laboratory Studies of Homogeneous and Heterogeneous Atmospheric Processes
Trace gas removal via reaction with OH
The degradation of most trace gases emitted into or generated in the atmosphere is initiated by the OH radical. The kinetics of this process defines the lifetime of pollutant emissions and thus to a large extent the distribution and concentrations of millions of trace gases. We use Pulsed Laser Photolysis set-ups (see Methods, Lab1 and 2) to derive temperature and pressure dependent rate coefficients for the reactions of the OH radical with many trace gases including those that have critical impact on e.g. the lifetime of reactive nitrogen in the atmosphere.:
Dulitz, K., Amedro, D., Dillon, T. J., Pozzer, A., and Crowley, J. N.: Temperature-(208-318 K) and pressure-(18-696 Torr) dependent rate coefficients for the reaction between OH and HNO3, Atmos. Chem. Phys., 18, 2381-2394, 2018.
Dillon, T. J., Dulitz, K., Gross, C. B. M., and Crowley, J. N.: Temperature-dependent rate coefficients for the reactions of the hydroxyl radical with the atmospheric biogenics isoprene, alpha-pinene and delta-3-carene, Atmos. Chem. Phys., 17, 15137-15150, 2017.
The hydroxyl radical, OH, is the primary oxidant in the Earth’s atmosphere, initiating the degradation of many common biogenic and anthropogenic trace gases. Most reactions of OH result in its removal from the radical pool, as long lived species which sequester HOx are formed. Some reactions, involving e.g. NOx, organic peroxy radical and peroxides can also regenerate OH (or HO2) resulting in radical recycling. The degree of radical recycling for any chemical system will impact on the levels of OH and thus on oxidation rates. We also explore the formation of OH in photochemical processes involving excited states. Pulsed Laser Photolysis set-ups (see Methods, Lab1 and 2) are the methods used in these studies.
Dillon, T. J., and Crowley, J. N.: Reactive quenching of electronically excited NO2∗ and NO3∗ by H2O as potential sources of atmospheric HOx radicals, Atmos. Chem. Phys., 18, 14005-14015, 10.5194/acp-18-14005-2018, 2018.
Groß, C. B. M., Dillon, T. J., and Crowley, J. N.: Pressure dependent OH yields in the reactions of CH3CO and HOCH2CO with O2, Phys. Chem. Chem. Phys., 16, 10990-10998, doi:10.1039/c4cp01108b, 2014.
Groß, C. B. M., Dillon, T. J., Schuster, G., Lelieveld, J., and Crowley, J. N.: Direct kinetic study of OH and O3 formation in the reaction of CH3C(O)O2 with HO2, The Journal of Physical Chemistry A, 118, 974-985, doi:10.1021/jp412380z, 2014.
Mineral aerosol and the chemistry of the free troposphere.
Mineral aerosol is the largest component of the coarse fraction of atmospheric aerosol, and with emissions of > 1 Tg per year is the most important aerosol (by mass) in the troposphere. The potential for mineral aerosol – trace gas interactions to modify the photochemistry of the free troposphere has been documented in several modelling studies, yet the physico-chemical parameters needed to describe such processes are very poorly characterised. We have embarked on a series of experiments to examine the interactions of mineral aerosol with a number of NOy trace gases such as HNO3 and N2O5. This research, presently employing an aerosol flow tube with chemiluminescence detection will be extended to allow detection of other trace gases (e.g. SO2, H2O2) by atmospheric pressure chemical ionisation mass spectrometry (see methods, Lab 4).
Tang, M. J., Schuster, G., and Crowley, J. N.: Heterogeneous reaction of N2O5 with illite and Arizona test dust particles, Atmos. Chem. Phys., 14, 245-254, 10.5194/acp-14-245-2014, 2014.
Greenhouse gases: Degradation mechanisms and lifetimes
The potential of a species to act as a greenhouse gas depends on its emission rate, the strength of its absorption features, and its atmospheric lifetime. Important loss processes may include: reaction with O3, OH, O(1D); photolysis; uptake to surfaces e.g. the ocean. We thus use a suite of experimental setups such as infrared spectroscopy, laser photolysis and wetted wall flow tubes (see Methods, Lab 1-3) to investigate the photochemical processes that lead to removal of greenhouse gases from the troposphere or stratosphere.
Bunkan, A. J. C., Srinivasulu, G., Amedro, D., Vereecken, L., Wallington, T. J., and Crowley, J. N.: Products and Mechanism of the OH initiated photo oxidation of perfluoro ethyl vinyl ether, C2F5OCF=CF2, Phys. Chem. Chem. Phys., 20, 11306-11316, 2018.
Srinivasulu, G., Bunkan, A. J. C., Amedro, D., and Crowley, J. N.: Absolute and relative-rate measurement of the rate coefficient for reaction of perfluoro ethyl vinyl ether (C2F5OCF=CF2) with OH, Phys. Chem. Chem. Phys., 20, 3761-3767, 10.1039/C7CP08056E, 2018.