Ultraviolet and infrared absorbtion by the ozone molecule

Theme: Earth, Atmosphere & Ocean Processes

Primary Supervisor:

Jonathan Tennyson

Physics and Astronomy, UCL

Jonathan Tennyson (UCL)

Secondary Supervisor:

Oleg Polyansky

Physics and Astronomy, UCL

Oleg Polyansky (UCL)
Additional Supervisor(s):

Sergey Yurchenko (Physics and Astronomy/UCL)

Project Description:

Ozone is present in low concentrations throughout the Earth’s atmosphere. In the troposphere ozone is a pollutant which largely results from human activity. Ozone is harmful at even trace concentrations. Conversely the stratospheric “ozone layer” provides an extremely important shield of solar radiation. Human activity has resulted in a significant reduction in stratospheric ozone and lead holes at the poles. Studies of atmospheric ozone concentrations rely heavily on the use of spectroscopic remote sensing from a mixture of ground-based, airborne and satellite instruments. These instruments observe the characteristic absorption features of ozone either in the infrared or the ultraviolet. Retrievals based on these observations require accurate laboratory data. The many studies of atmospheric currently require data for both ultraviolet and infrared accurate to 1% or better. Unfortunately, there are many measurements showing systematic differences between atmospheric studies performed at infrared and ultraviolet wavelengths at the 4 to 5 % level. While laboratory measurements of the ultraviolet cross sections show a measure of agreement, those for the infrared do not. A recent analysis concluded that for the key 10 micron region agreement between measurements was only at best 4% with intensity discrepancies much higher than this. We will use high accuracy, first principles quantum mechanical methods to compute the transition intensities for both the IR and UV portions of the spectrum. For the infrared region, methods of computing high accuracy dipole moment surfaces already used successful for water and CO2, will be employed. These will be combined with measured transition frequencies to complete line lists with intensities accurate to about 0.5%. New methodologies will be developed to transfer the experience gained computing infrared vibration-rotation intensities (which require electronically diagonal dipole moments) to ultraviolet electronic transitions.

Policy Impact of Research:

Results will be important for a range of atmospheric studies. They will be made widely available via the web, databases and submitted for inclusion in standard compilations used for atmospheric studies such as HITRAN. HITRAN will be a project partner on the proposal and undertake independent evaluation of the results.

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