Report on SPARC/IGAC working group on ozone photolysis

A. R. Ravishankara (ravi@al.noaa.gov) and R. A. Cox

 

The hydroxyl radical is one of the most important reactive species in the atmosphere. It is the agent that leads to the removal of a large number of chemicals in the atmosphere and also transforms many other atmospheric species, hence nick-named Mother Nature’s detergent. The primary pathway by which OH is produced in the atmosphere is via the photodissociation of ozone in the ultraviolet region to produce electronically excited oxygen atoms O(¹D) followed by the reaction of this species with water (or other species). Even though this pathway is considered to be well established (it is in all atmospheric chemistry textbooks), the quantum yield for the production of O(¹D) (i.e., the fraction of ozone molecules absorbing light that dissociate to give this species) in ozone photolysis was uncertain. The quantum yield for O(¹D) production as a function of wavelength and temperature is a key input for atmospheric modelling calculations. In the past few years, a large number of investigators have measured this quantity using diverse methods. The result of these studies have shown that the data currently used in models is erroneous at wavelengths beyond ~310nm. To provide the modelling community with the best possible information, the SPARC/IGAC task on ozone photochemistry under the Laboratory Studies project brought together most of the principal scientists involved in these investigations to carefully analyse the available data and come up with the best possible recommendation for the quantum yields. The working group consists of the following scientists:

1. Y. Matsumi, University of Nagoa, Japan (Chair of this group),
2. F. J. Comes, Frankfurt University, Germany,
3. G. Hancock, Oxford University, UK,
4. A. Hofzumahaus, KFA, Germany,
5. A. J. Hynes, University of Miami, USA,
6. M. Kawasaki, Kyoto University, Japan, and
7. A. R. Ravishankara, NOAA, USA.

The group did a great deal of work through electronic communication and finally met in Oxford, UK, in September of 1999. The meeting was extremely successful. It led to a lot of checks and inter-comparisons. The finalised recommendation is being derived and is being written up for publication. It will be available to the atmospheric chemistry community in a few months. It will be submitted to a refereed journal for publication. Also, all the supporting material, as well as the final write-up, will be in the SPARC data center.