Arctic ozone depletion in 2019/20: Roles of chemistry, dynamics and the Montreal Protocol

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.