New Insights into the Role of Stabilized Criegee Intermediates in Tropospheric Chemistry from Direct Laboratory Studies: Volume 2: Organic Oxidation and Multiphase Chemistry

It has been known for some time that the ozonolysis of alkenes plays a role in the oxidizing capacity of the Earth’s atmosphere. On reaction, Criegee intermediates (CIs) are formed whose unimolecular decomposition can yield HO radicals and be a source of this key oxidant both in the day and night. However, direct determination of rate coefficients for the reaction of these CIs with water and other species present in the atmosphere have been elusive until ground-breaking experiments in 2012 allowed direct preparation of these intermediates. In this chapter, the various methods that have been used to prepare CIs are reviewed and rate coefficients, determined using these techniques, are collated. Recent direct kinetic investigations (and accompanying product studies) have shown that even with a modest steady-state concentration of around 1×104 molecule cm−3, these CIs make a nonnegligible contribution to the oxidizing capacity of the terrestrial boundary layer. CIs oxidize SO2 and produce a significant amount of SO3, and subsequently H2SO4, which is a key species in atmospheric particle nucleation. Their reactions with carboxylic acids, carbonyl compounds, peroxy radicals, and hydroperoxides are likely to yield highly oxygenated species which may lead to nucleation, secondary organic aerosol formation, and radiative forcing of climate change (cooling) on regional and global scales. Atmospheric model scenarios are integrated to provide illustrative potential impacts of these species. This chapter also collates spectroscopic data on these CIs as well as kinetic and product information.