New instrumentation has been developed for the detection of Criegee intermediates (CIs) under a wide range of temperature and pressure conditions. This instrumentation has been applied to the investigation of CI reactions with trifluoracetic acid and some small alcohols, both of which are present as trace atmospheric gases. This work has demonstrated that the rate of these reactions will change in a complex fashion as a function of tropospheric altitude. We have been able to use computer simulations to model this behaviour, and to predict the complex temperature dependencies of many different CIs with trace tropospheric constituents.
As an extension to this, we have used a combined experimental and computational approach to interrogate the chemistry of many different Criegee intermediates with ranging chemical properties, such as chemical substitution and chemical conjugation. We have used this approach to evaluate structure-activity relationships, for example, for CIs with atmospheric alcohols. Alcohol tropospheric concentrations vary by several orders of magnitude, with higher concentrations where biofuel use is prevalent. CI reactions with alcohols is a significant tropospheric source of alpha-alkoxylalkylhydroperoxides. Using this data we are building taxonomic groups for CIs.
Criegee intermediates react with SO2 to generate SO3, which can react with water to form sulphuric acid, ultimately resulting in aerosol formation. We have targeted and interrogated key CI reactions which lead to the formation of SO3 in the troposphere. Many of these SO3 forming reaction occur incredibly quickly, with effective reaction rates limited only by the rate at which the gases collide. Thus, these reactions, in particular urban environments, may be efficient at inducing aerosol formation. Future work is to experimentally identify key spectral fingerprints for precursors to CI-induced aerosol nucleation.
This work has led to two high quality scientific publications so far.
‘Criegee intermediate alcohol reactions, a potential source of functionalized hydroperoxides in the atmosphere’ M.R. McGillen, et al. J.M. Beames, N. Watson, A.J. Orr-Ewing ACS Earth Space Chem. 1 664 (2017)
‘Temperature Dependence of the Rates of Reaction of Criegee Intermediates with Trifluoroacetic Acid’ R. Chhantyal-Pun, et al. J.M. Beames, A.J. Orr-Ewing Angew. Chem. Int. Ed. 56 9044 (2017)
Data has been generated for two more scientific publications, one of which has been submitted for peer-review (not included in above text as they are still confidential at the time of this report).
This work has been disseminated through oral presentations at research conferences, and through invited seminars at a range of academic institutions including, but not limited to, the University of Cambridge and Xiamen University (China).
This work has led to the creation of new instrumentation at Cardiff University, which will continue to be used moving forward from the period of this grant, generating new and exciting scientific data.
Similarly, the PI has advanced his computational chemistry skills, and will use this knowledge in tackling similar atmospheric chemistry issues beyond the time period of this research grant.
