Arctic Ozone Depletion in 2019/20: Roles of Chemistry, Dynamics and the Montreal Protocol

We use a three-dimensional 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 modeled chemical column ozone loss reached 78 DU (local maximum loss of similar to 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 2 decades ameliorated the polar cap ozone depletion in March 2020 by similar to 20 DU.

Automated summary

Using a three-dimensional chemical transport model and satellite observations, researchers investigated the Arctic ozone depletion in winter/spring 2019/20 and compared it with previous years. Persistently low temperatures led to extensive chlorine activation, while weak dynamical replenishment played a key role in causing very low column ozone values in the region. The study also showed that the gradual recovery of the ozone layer over the past two decades alleviated the polar cap ozone depletion in March 2020 by around 20 DU.