Gas-Phase Ozonolysis of Alkenes: Intermediates and Stable Products in the Troposphere

Lead Research Organisation: University of Reading
Department Name: Chemistry


This proposal focuses on the chemistry of the reactions of ozone with unsaturated compounds (alkenes). These reactions are very important in the chemistry of the lowest region of the atmosphere, known as the boundary layer. Chemistry in this region is mainly the removal of organic compounds emitted at the surface either naturally or anthropogenically. This chemistry has been described as being akin to a low-temperature flame. The reactions of ozone with alkenes contribute to this removal directly, because the reactions destroy alkenes. However, they also play other important roles: the reactions generate new classes of compounds, particularly oxygenated compounds such as alkdehydes (RCHO); they generate OH radicals, which are the major initiators of oxidation in the lower atmosphere; intermediates in the reactions can oxidise SO2 to SO3, contributing to acid rain formation and the formation of aerosol particles; and they also lead to aerosol through the formation of secondary organic aerosol. In this proposal, the main focus of the work is on characterising the key intermediates in the reaction (the so-called Criegee intermediate and the vinyl hydroperoxide intermediate) and accurately determining yields for the products of secondary reactions. The main motivation for the work is to properly understand the role that OH formation has in atmospheric chemistry, but the proposed experiments also have important implications for the other aspects of ozone-alkene atmospheric chemistry summarised above. Some experiments will be carried out in collaboration with Dr Kevin Smith at the Molecular Spectroscopy Facility of the Rutherford Appleton Laboratory, where a flow tube interfaced to an infrared spectrometer will be improved. These experiments will allow the intermediates to be examined as a function of time and their spectroscopy and kinetics can be characterised. Other experiments will be carried out at the School of Chemistry at the University of Reading. These will focus on obtaining accurate yields of secondary aldehydes and organic acids, in the reactions, and will be carried out in static reaction chambers coupled to detection by the analytical techniques gas chromatography and infrared spectroscopy. These studies will test our understanding of the reaction mechanisms and improve our knowledge of the yields of radical formation in the reactions. Finally, in an agreed collaboration with Dr Mike Jenkin of Imperial College, we will use the results in combination with the most up to date findings in the literature to improve the implementation of the mechanism of ozone-alkene chemistry in the Master Chemical Mechanism, a description of the chemistry of the lower atmosphere that is an important tool to aid policy in the area of air quality.


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Description FTIR coupled to a long-path cell was used to determine branching ratios in the reactions of acyl RC(O)O2 (R = CH3, CH3CH2 and (CH3)2CH) with HO2. These reactions are important reactions in ozonolysis systems as they are a source of organic acids (very important in SOA formation in the ozonolysis of terpenes) regenerate O3 and are now known to generate OH radicals (a known product of ozonololysis). Moreover, the reactions are of key importance in boundary layer chemistry as a result of other sources of RC(O)O2. Our results confirm a study by Jenkin et al. published soon after the project started that OH radicals are generated in the reactions for R=CH3. For R=CH3CH2 and (CH3)2CH - which have not been previously studied - we were also able to show that the OH formation channel is important (30-40 %). These are important results, as they imply that this class of reactions has a significant non-chain terminating component, which must be included in tropospheric models.

We also examined the mechanisms of the reactions of ozone with a range of alkenes, but with particular emphasis on cyclohexene, methylcyclohexene and methylenecyclohexane. These compounds are sufficiently simple to provide insights in to the general ozonolysis mechanism, but can also act as models for the more complex (and important) terpene ozonolysis systems. A wide range of secondary products were determined, including acids and carbonyl species (and compounds containing both functionalities). Yields were studied as a function of concentration and relative humidity, and concentration and nature of OH scavenger. Important results include: the determination of key branching ratios for processes observed in these systems (for example the primary ozonide resulting from the ozonolysis of methylcyclohexene was shown to decompose to give the more substituted Criegee intermediate with 70 % efficiency); the development of quantitative relationships between the products of the ozonolysis of methylcyclohexene and methylenecyclohexane; development of a detailed quantitative mechanism for cyclohexene ozonolysis that can form the basis of mechanisms of more complex systems.

Attempts to detect the Criegee intermediate by Fourier Transform Infrared Spectroscopy in a flow tube on the timescale expected from previous work were unsuccessful, but it was not clear why this was the case.
Exploitation Route The findings on the branching ratios for OH formation could be used in atmospheric models.

The research on the ozonolysis of simple cyclic alkenes provides a basis for other studies on more complex terpenes found in the atmosphere.
Sectors Environment

Description Engagement with school pupils and their teachers has helped in th epublic understanding of science and the environment.
First Year Of Impact 2006
Sector Education
Impact Types Societal

Description Teaching Collaboration between University of Reading and Nanjing University of Science and Technology 
Organisation Nanjing University of Information Science and Technology (NUIST)
Country China 
Sector Academic/University 
PI Contribution I employed Dr Yan Ma as a PDRA in grant NE/D013569/1. When she left she took up a lectureship at Nanjing University of Information Science and Technology. Very soon after her appointment at NUIST we worked together to start a 4+1 arrangement for NUIST Applied Chemistry students to carry out an MSc in Chemical Research at the University of Reading, with the first students starting in 2010. This further developed into a 3+1 arrangement, with NUIST students carrying out their final year at Reading. The first cohort of 16 students came to Reading in 2014. In October 2015, the NUIST-University of Reading Academy was created with students involved from Chemistry, Economics, Mathematics and plans for joint Meteorology degree.
Collaborator Contribution See above.
Impact The NUIST-University of Reading Academy was created in October 2015.
Start Year 2008
Description Visit to Reading Chemistry Department by a number of schools 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact Workshop for school pupils.
Year(s) Of Engagement Activity 2006