Near complete local reduction of Arctic stratospheric ozone by severe
chemical loss in spring 2020
Abstract
In the Antarctic ozone hole, ozone mixing ratios have been decreasing to
extremely low values of 0.01-0.1 ppm in nearly all spring seasons since
the late 1980s, corresponding to 95-99 % local chemical loss. In
contrast, Arctic ozone loss has been much more limited and mixing ratios
have never before fallen below 0.5 ppm. In Arctic spring 2020, however,
ozone sonde measurements in the most depleted parts of the polar vortex
show a highly depleted layer, with ozone loss averaged over sondes
peaking at 93 % at 18 km. Typical minimum mixing ratios of 0.2 ppm were
observed, with individual profiles showing values as low as 0.13 ppm (96
% loss). The reason for the unprecedented chemical loss was an
unusually strong, long-lasting and cold polar vortex, showing that for
individual winters the effect of the slow decline of ozone-depleting
substances on ozone depletion may be counteracted by low temperatures.