Details of Award
NERC Reference : NE/K005820/1
Peroxy Radical Photolysis and its Impact on Atmospheric Chemistry (PRiPIAC)
Grant Award
- Principal Investigator:
- Dr MA Blitz, University of Leeds, Sch of Chemistry
- Co-Investigator:
- Dr T Ingham, University of Leeds, Sch of Chemistry
- Co-Investigator:
- Professor DE Heard, University of Leeds, Sch of Chemistry
- Co-Investigator:
- Dr L Whalley, University of Leeds, Sch of Chemistry
- Grant held at:
- University of Leeds, Sch of Chemistry
- Science Area:
- Atmospheric
- Overall Classification:
- Atmospheric
- ENRIs:
- Environmental Risks and Hazards
- Global Change
- Pollution and Waste
- Science Topics:
- Atmospheric Kinetics
- Land - Atmosphere Interactions
- Radiative Processes & Effects
- Tropospheric Processes
- Climate & Climate Change
- Abstract:
- Unpolluted, forested regions occupy a significant fraction of the planet's surface, and are characterised by large emissions of biogenic VOCs, for example isoprene. Constrained box models using the detailed Master Chemical Mechanism and Earth System Models using more simplistic schemes, calculate low concentrations of OH owing to the rapid removal by reaction with reactive plant emissions. Recent measurements in tropical regions by several groups show these calculations to be too low by up to an order of magnitude, and hence overestimate the lifetime of methane, a greenhouse gas, and underestimate the rate of chemical oxidation leading to secondary products including organic aerosols. These findings also extend to regions that are influenced by man's activities, where ozone and other products harmful to health are generated via chemistry initiated by OH. There is currently no consensus on the source of this missing OH, with one suggested mechanism by Peeters et al., based on theoretical, computer calculations, being inconsistent with evidence obtained in the laboratory and field measurements of other key species. This is a very serious shortcoming when considering biosphere-atmosphere-climate feedbacks for these regions, and calculating the regional impact on climate of deforestation or changes in land-use. The outcome of this project will be an experimentally proven and novel photochemical mechanism capable of generating significant additional OH, which when incorporated into Earth System Models will enable the relationship between plant emissions and the response of the atmospheric chemistry system to be properly represented. In this proposal, we suggest that the missing source of OH is not just a product of a chemical reaction, but rather the solar photolysis of peroxy radicals, which themselves are generated following the reaction of OH with the primary emissions, for example isoprene and other reactive hydrocarbons . This hypothesis represents a paradigm shift in our understanding of atmospheric chemistry. Preliminary experiments measuring the yield of OH following photolysis of peroxy radicals undertaken in our laboratory have provided evidence that this process is occurring. Contrary to expectations, OH is observed following photolysis at wavelengths that are active in the atmosphere. The preliminary OH yields obtained at a very limited number of wavelengths have been crudely parameterized and fed into an atmospheric model, and shown that it is already a more significant source of additional OH than the Peeters' mechanism. However, further OH production is still required to match observed OH. It is known that peroxy radicals have electronic absorption bands in the near infrared, and while it has never been demonstrated that near infrared radiation can photolyse RO2 to OH, these channels are thermodynamically possible and we hypothesise that this may explain more of the missing OH. This proposal aims to make measurements of OH yields following peroxy radical photolysis, over a wide range of wavelengths, from the ultraviolet to the near infrared, for peroxy radical species derived from the oxidation of relevant primary emissions. The range of species is extensive enough that predictions can be made on structurally similar species that are not included in this proposal. An extensive set of experiments will also be made to measure the absorption cross-sections of a range of RO2, and at longer wavelengths we will utilise the sensitivity of the Leeds FAGE instrument to measure the OH photolysis yields. In addition, by locating a cold trap beyond the photolysis region we will collect the co-products formed alongside OH, for subsequent identification using conventional analytical techniques. As the OH product from peroxy radical photolysis is unexpected, we will explore the mechanism of its formation by selectively replacing certain hydrogen atoms (H) in the peroxy radical, with its heavier deuterium (D) analogue.
- NERC Reference:
- NE/K005820/1
- Grant Stage:
- Completed
- Scheme:
- Standard Grant (FEC)
- Grant Status:
- Closed
- Programme:
- Standard Grant
This grant award has a total value of £485,521
FDAB - Financial Details (Award breakdown by headings)
| DI - Other Costs | Exception - Other Costs | Indirect - Indirect Costs | DA - Investigators | DI - Staff | DI - Equipment | Exception - Staff | DA - Estate Costs | DA - Other Directly Allocated | DI - T&S |
|---|---|---|---|---|---|---|---|---|---|
| £71,586 | £10,525 | £111,800 | £46,800 | £99,004 | £16,060 | £41,266 | £64,848 | £16,102 | £7,530 |
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