In 1995, that instrument was no longer working, but balloon-borne instruments measured near-record values below 100 Dobson units
in the atmosphere above the South Pole.
He and his colleagues recorded a low of 100 Dobson units
of ozone on Sept.
scientists tracking conditions at the South Pole measured ozone concentrations of 98 Dobson units
They recorded concentrations as low as 110 Dobson units
(DU) in September and 120 DU in October 1958.
The instrument measured the 2011 ozone hole at its deepest at 95 Dobson units
Satellite- and balloon-borne instruments showed that the amount of ozone over Antarctica bottomed out in early October at a value of 90 to 92 Dobson units
, the same as last year.
There was about half as much ozone loss as in the Antarctic and the ozone levels remained well above 220 Dobson units
, which is the threshold for calling the ozone loss a 'hole' in the Antarctic - so the Arctic ozone loss of 2011 didn't constitute an ozone hole," Strahan said.
6, the balloon ozone sensors detected only 90 Dobson units
of ozone, a reading corroborated by a ground-based spectrometer.