Arctic ozone depletion in 2019/20: Roles of chemistry, dynamics and the
Montreal Protocol
Abstract
We use a 3-D chemical transport model and satellite observations to
investigate Arctic ozone depletion in winter/spring 2019/20 and compare
with earlier years. Persistently low temperatures caused extensive
chlorine activation through to March. March-mean polar-cap-mean modelled
chemical column ozone loss reached 78 DU (local maximum loss of
~108 DU in the vortex), similar to that in 2011.
However, weak dynamical replenishment of only 59 DU from December to
March was key to producing very low (<220 DU) column ozone
values. The only other winter to exhibit such weak transport in the past
20 years was 2010/11, so this process is fundamental to causing such low
ozone values. A model simulation with peak observed stratospheric total
chlorine and bromine loading (from the mid-1990s) shows that gradual
recovery of the ozone layer over the past two decades ameliorated the
polar cap ozone depletion in March 2020 by ~20 DU.