Reconciliation of halogen-induced ozone loss with the total-column ozone record (original) (raw)
The observed depletion of the ozone layer is attributed to anthropogenic 1 halogens, but the precision of this attribution is complicated by natural 2 dynamical variability (year-to-year meteorological variations) and by changes 3 in tropospheric ozone, leaving key aspects of the observed total ozone record 4 unexplained. These include inter-hemispheric differences in the response to 5 the Mount Pinatubo volcanic eruption, the lack of a decline prior to 1980 and 6 of any long-term decline in the tropics, and the apparent delay in ozone 7 recovery despite the significant decline of stratospheric halogen loading since 8 the late 1990s. Here we use a chemistry-climate model constrained by 9 observed meteorology to remove the effects of dynamical variability and to 10 estimate changes in tropospheric ozone. Ozone loss is shown to closely follow 11 stratospheric halogen loading, with pronounced enhancements in both 12 hemispheres following the volcanic eruptions of El Chichon and, especially, 13 Mount Pinatubo. Approximately 40% of the long-term non-volcanic loss is 14 found to have occurred by 1980. Long-term ozone loss is found in the tropical 15 stratosphere, but is masked in the column by tropospheric increases. Ozone 16 loss has declined by over 10% since stratospheric halogen loading peaked in 17 the late 1990s, indicating that recovery of the ozone layer is well underway. 18 19 Anthropogenic emissions of halogenated (principally chlorine) species have led to 20 an observable depletion of the ozone layer 1. Ozone depletion has been a matter of 21 wide public concern because of its implications for human and ecosystem health 2. 22 As a result of comprehensive controls on ozone-depleting substances, stratospheric