In regions with high VOC concentrations and low NOx concentrations, such as the Danum Valley in Borneo (pristine tropical rainforest with high concentrations of isoprene) and the Pearl River Delta, China (urban region with a wide range of VOCs and low NOx), modelled values of [OH] are often much lower than measured values. One reason for this could be a significant missing source of OH. It has been proposed that photolysis of peroxy radicals (RO2) could be an important part of this missing source.
A number of experiments have been set up at the University of Leeds to test this hypothesis. Preliminary findings indicate that photolysis of isoprene derived RO2 radicals at atmospherically-relevant wavelengths produces OH.
Absorption spectra of photolysis products
A multipass absorption spectrometer is being developed in the Dainton laboratory at the University of Leeds. The instrument will record time resolved absorption spectra of RO2 photolysis products.
FAGE Studies of OH
The yield of OH from RO2 photolysis is being studied using the FAGE technique. RO2 radicals are produced by reaction of OH with hydrocarbons, and are photolysed in the wavelength ranges 300-450 nm and 1100-1700 nm. OH concentrations are recorded as the photolysis wavelength is varied, to produce an action spectrum. Potential interferences in FAGE will be investigated.
The RO2 cross section data and OH yields will be included in photolysis and box models to test the impact of the laboratory measurements on the atmospheric concentrations of OH and HO2, in key regions such as the Borneo rain forest.