Welcome to the CORAXX Project Page


(COsmic Radiation Aircraft eXposure eXperiment)


Max-Planck-Institute
for Chemistry


Oxford Radiocarbon
Accelerator Unit

Department of Nuclear Physics
Comenius University
Bratislava, Slovakia

A joined project of Lufthansa, the Max-Planck-Institute for Chemistry, the Oxford Radiocarbon Accelerator Unit (special funding by NERC), and the Department of Nuclear Physics of the Comenius University, Bratislava, Slovakia.

The most important oxidant in the atmosphere, determining the self-cleansing capacity of the atmosphere is the hydroxyl radical (OH). Present knowledge about the atmospheric distribution and seasonal cycle of the OH radical is mainly based on complex model calculations, since measurements of OH on the global scale are hampered by its high reactivity. Its resulting short lifetime and low concentration not only make detection difficult, but render obtaining a global picture nearly impossible. Although chemistry-transport models are continuously being improved by implementing refined transport schemes, more complete chemistry parameterizations, cloud effects, etc., there is still a considerable degree of uncertainty about OH seasonality and distribution. Because of the great importance of OH in the chemistry of the atmosphere independent verification of the calculated OH distribution is therefore necessary. This is usually performed in an indirect way by measurements of tracers which react with OH. Knowing the emission-/production-rates of the tracer and it's reaction rate with OH, the amount of OH can in principle be derived from measurements of the atmospheric concentration of the tracer. One particularly promising tracer candidate is 14CO. Most 14CO present in the atmosphere is the result of the interaction (nuclear reactions) of cosmic particle radiation (mainly protons) with the atmosphere. The average lifetime of a 14CO molecule in the atmosphere is roughly 3 months before it is oxidized with OH forming 14CO2. The flux of the 14CO forming cosmic ray particles (and therefore the 14CO formation itself) is influenced by the properties of the solar wind plasma (which change periodically with a period of 11 years) and the geomagnetic field, and is further dependent on the cross sections of various nuclear reactions involved. As a consequence, the 14CO production rate increases with latitude and height (see Figures 1 and 2).


Figure 1: Annual zonal mean galactic cosmic ray induced 14CO production rate (GCR, shaded) and annual zonal mean solar proton event induced 14CO production rate (SPE, contour lines). The unit is 10-3 molec g-1 s-1 normalized to a global average production rate of 1 molec cm-2 s-1. (Image taken from: Patrick Jöckel, Cosmogenic 14CO as tracer for atmospheric chemistry and transport, Dissertation submitted to the Combined Faculties for the Natural Sciences and for Mathematics of the Rupertus Carola University of Heidelberg, Germany for the degree of Doctor of Natural Sciences, 2000. -download- )


Figure 2: Vertically integrated annual mean cosmogenic production rate of 14CO. The unit is 14CO-molecules cm-2 s-1 normalized to a global average production rate of 1 14CO-molecule cm-2 s-1 in an idealized static atmosphere of constant depth (1033 g cm-2). (Image taken from: Patrick Jöckel, Cosmogenic 14CO as tracer for atmospheric chemistry and transport, Dissertation submitted to the Combined Faculties for the Natural Sciences and for Mathematics of the Rupertus Carola University of Heidelberg, Germany for the degree of Doctor of Natural Sciences, 2000. -download- )

However, the rather complex interactions show that an accurate determination of the 3-dimensional 14CO production rate distribution in the atmosphere and its temporal variation is not straightforward. Model calculations are difficult and still imply uncertainties, epecially concerning the global average production rate of 14CO in the atmosphere. This is the starting point of the joined (Lufthansa and MPI for Chemistry) project CORAXX (COsmic Radiation Aircraft eXposure eXperiment) which is designed to measure directly the cosmogenic 14CO production rate. Pressurized air cylinders on board an aircraft are exposed to the natural cosmic radiation.


Figure 3: Schematic diagram of CORAXX.
14CO is formed inside the cylinders but not oxidized due to the lack of photochemically produced OH (the necessary light is absent). The amount of 14CO formed during the exposure time will be compared to theoretical calculations. Since the 14CO production rate depends on the location (latitude, longitude, and pressure level), the flight path of the aircraft has to be known at any time during exposure.
For further information please contact Patrick Jöckel (joeckel@mpch-mainz.mpg.de) or Carl Brenninkmeijer (leader of the project) (carlb@mpch-mainz.mpg.de).
This page was last modified on 05 Jun 2008.
If you have comments or suggestions, e-mail me at joeckel@mpch-mainz.mpg.de  !
You can visit my home-page at http://www.mpch-mainz.mpg.de/~joeckel