Trends in the vertical distribution of ozone: Assessment and implications in terms of ozone recovery

The successful implementation of the Montreal Protocol has led to reductions in stratospheric halogen loading, which is expected to result in less chemical depletion of ozone and thus increased stratospheric ozone amounts [WMO, 2011]. To unambiguously identify a positive ozone response directly attributable to declining halogen levels, consistent long-term ozone profile observations are required. Although near-global satellite observations of the ozone profile have been made since 1978, no single instrument has covered this entire period, meaning that merged data series combining several instrument records are required to fully understand long-term ozone changes.

All available long-term data sets are analyzed for trends in the period 1979-2012. The data sets are based on a varying combination of instruments including SBUV/2, SAGE-2, HALOE, UARS-MLS, OSIRIS, SAGE-3, GOMOS, ACE-FTS, and Aura-MLS. The analyses reveal that all data sets represent seasonality and interannual variability well, with those data sets based on the same instrument set tending to be more similar, despite different merging techniques being used. A multiple linear regression analysis reveals that long-term ozone trends are similar in the period prior to 1997, but show more diversity for the period since 1998. This is likely a result of the different instruments used to construct each data set, which vary more in the latter period. These results have important implications in terms of the detection of ozone recovery resulting from the reduction in stratospheric halogen loading.

This work was done as part of the SI2N (Stratosphere-troposphere Processes And their Role in Climate (SPARC), the International Ozone Commission (IOC), the ozone focus area of the Integrated Global Atmospheric Chemistry Observations (IGACO-O3), and the Network for Detection of Atmospheric Composition Change (NDACC) - SPARC/IOC/IGACO-O3/NDACC) initiative.