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"We knew from observations dating from 1987, that
the high ozone loss was linked with high [levels of] chlorine monoxide,
but we had never actually detected the ClOOCl before," Stimpfle said
in an interview. The common name atmospheric scientists use for ClOOCl,
he said, is "chlorine dimer"--two identical chlorine-based molecules,
ClO or chlorine monoxide--bonded together. The rare dimer exists only
in the particularly cold stratosphere over polar regions where
chlorine monoxide levels are relatively high. "Most of the chlorine in
the stratosphere," Stimpfle adds, "continues to come from
human-induced sources."
ClOOCl triggers ozone destruction, he explains, in
three basic steps:
"You are now back to where you started with respect
to the ClOOCl molecule," Stimpfle says, "but in the process you have
converted two ozone molecules into three oxygen molecules. This is the
definition of ozone loss."
These results were acquired during a joint
US-European science mission, SOLVE/THESEO-2000, based in Kiruna,
Sweden, from November 1999 to March 2000. A NASA ER-2
aircraft--essentially a U2--flew into Russian air space for the first
time with the cooperation of Russian authorities, Stimpfle says, for
the purpose of collecting scientific data of interest to the world
community. The instrument used to measure ClOOCl was designed to
detect several important inorganic chlorine species and was housed in
a wing pod of the ER-2. This work was funded by the NASA Upper
Atmospheric Research Program. |
