Routine ground-based measurements of total ozone column (TOC), as well as ozone profile soundings started in the late 1960s in Germany. The resulting ozone and temperature records at Hohenpeissenberg and Berlin / Potsdam / Lindenberg show long-term changes similar to other stations in Central Europe, and to the changes seen globally. Following the increase of ozone depleting substances (ODS), stratospheric ozone has declined from the 1960s until the 1990s. Since about 2000, ozone has leveled or slightly increased, consistent with declining amounts of ODS. The stratosphere has been cooling and the troposphere has been warming, in agreement with general expectations due to increasing greenhouse gas concentrations. The clearest signs of recovering ozone are seen around 40 km altitude. Two factors contribute to this increase: the decrease of stratospheric chlorine loading and cooling of the upper stratosphere, which slows gas-phase ozone destruction cycles, and enhances the ter-molecular reaction producing ozone. Tropospheric ozone has increased substantially from the 1960s to the early 1990s. Since then, it has remained more or less constant, on a level higher compared to the 1960s and 1970s. Particularly low tropospheric ozone was observed in 2020, due to reduced precursor emissions during the COVID-19 related lockdowns. The atmospheric concentrations of greenhouse gases will likely continue to rise, while the concentrations of ozone depleting substances are expected to slowly decline. To see how the atmosphere responds, and to help understand future changes, continued monitoring will be required for many years to come, both over Germany and worldwide.

Throughout spring and summer 2020, ozone stations in the northern extratropics recorded unusually low ozone in the free troposphere. From April to August, and from 1 to 8 kilometers altitude, ozone was on average 7% (~4 ppbv) below the 2000 to 2020 climatological mean. Such low ozone, over several months, and at so many stations, has not been observed in any previous year since at least 2000. Atmospheric composition re-analyses from the Copernicus Atmosphere Monitoring Service and simulations from the NASA GMI model indicate that the large 2020 springtime ozone depletion in the Arctic stratosphere has contributed less than one quarter to the observed tropospheric anomaly. The observed anomaly is consistent with two recent model simulations, which assume emission reductions similar to those caused by the COVID-19 crisis. COVID-19 related emission reductions appear to be the major cause for the observed low free tropospheric ozone in 2020.

The recent Assessment of Standard Operating Procedures for OzoneSondes (ASOPOS 2.0; WMO/GAW Report #268) addressed questions of homogeneity and long-term stability in global electrochemical concentration cell (ECC) ozone sounding network time series. Among its recommendations was adoption of a standard for evaluating data quality in ozonesonde time-series. Total column ozone (TCO) derived from the sondes compared to TCO from Aura’s Ozone Monitoring Instrument (OMI) is a primary quality indicator. Comparisons of sonde ozone with Aura’s Microwave Limb Sounder (MLS) are used to assess the stability of stratospheric ozone. This paper provides a comprehensive examination of global ozonesonde network data stability and accuracy since 2004. Comparisons with Aura OMI TCO averaged across the network of 60 stations are stable within about +/-2% over the past 18 years. Sonde TCO has similar stability compared to three other TCO satellite instruments, and the stratospheric ozone measurements average to within +/-5% of MLS from 50 to 10 hPa. Thus, sonde data are reliable for trends, but with a caveat applied for a subset of stations in the tropics and subtropics for which a sudden post-2013 TCO “dropoff” of ~3-4% was reported previously (Stauffer et al., 2020). The dropoff is associated with only one of two major ECC instrument types. A detailed examination of ECC serial numbers pinpoints the timing of the dropoff. However, we find that overall, ozonesonde data are stable and accurate compared to independent measurements over the past two decades.