To improve the understanding of the oxygen atoms and OH radicals production rate in the troposphere.
The oxidising efficiency of the troposphere is mainly determined by the concentration of hydroxyl radicals (OH). These are primarly formed by the reaction of 0 (1D) atoms with water vapour. The 0 (1D) atoms are produced by the photolysis of ambient ozone with solar radiation in the spectral range of UV-B (280-320 nm). Thus, any change of solar UV-radiation has a major impact on the global oxidation potential of the atmosphere. At present, there is a deficiency of experimental field data on the tropospheric formation rate J (01D) of 0 (1D) atoms from ozone photolysis by solar radiation. Furthermore, the photochemistry of ozone at wavelength in the UV-B appears to be not well established.
Continuous field measurements of J (01D), O3 and H2O will be carried out in order to establish a database to obtain diurnal and seasonal variations of the 0 (1D) and OH production rates at 50° North. Its relationship to concurrently observed meteorological parameters, such as atmospheric aerosol or clouds, will be investigated and compared with theoretical J (01D) predictions from radiation flux models. A new chemical flow actinometer will be constructed for direct continuous and absolute measurements of J (01D). It will complement the radiometric J (01D) measurement techniques used for the long-term measurements.
Laboratory work will be carried out to explore newly discovered spin forbidden channels in the photodissociation of O3 near 310 nm. In particular, the quantum yield of 0 (1D) will be remeasured using a novel laser detection technique for direct 0 (1D) detection. The dependence on wavelength and temperature will be studied at conditions of tropospheric interest. J (01D) field measurements by chemical actinometry will be used to test the consistency of experimental J (01D) observations with the laboratory 0 (1D) quantum yield data and their temperature dependence. Furthermore, the relative contributions of the O3 photodissociation channels to the formation of 0 (3P), 0 (1D), and excited singlet O2 will be completely specified for absorption wavelengths near 310 nm.
Funding SchemeCSC - Cost-sharing contracts
OX1 3QZ Oxford