Assuring Quality Data from Ozonesonde Time-series: Experimental Framework and Recent Accomplishments

<jats:p>The electrochemical concentration cell (ECC) ozonesonde is a small instrument flown on weather balloons coupled to radiosondes at ~60 stations. Ozone concentrations, pressure, temperature and humidity are measured from surface to ~10 hPa. Although designed 50-plus years ago, ozonesondes remain a crucial technology for global ozone-observations. Not limited by cloud interferences, ozonesondes record ozone partial pressures with 100-150 m vertical resolution, supplying profiles for satellite retrievals and validation of other ozone-measuring instruments. Sondes provide the longest record of ozone vertical trends, supporting the Montreal Protocol (UNEP, 2020; WMO/UNEP, 2022) and Tropospheric Ozone Assessment Report (Thompson et al., 2025; Van Malderen et al., 2025a,b). The drawback to sondes is that each launch uses a new instrument, requiring protocols for preparation and data processing to ensure that all measurements are comparable. The ozonesonde community employs a three-pronged strategy to optimize data quality and to correct for inhomogeneities over time. First, JOSIE (Jülich Ozonesonde Intercomparison Experiment; 1996-) laboratory tests intercompare sondes of varying manufacture in a World Calibration Center for Ozonesondes. Second, since 2004 an ASOPOS (Assessment of Standard Operating Procedures of Ozonesondes) panel evaluates JOSIEs and issues standard operating procedures (SOP) with WMO (GAW Report No. 268, 2021). Third, an O3S-DQA (Ozonesondes Data Quality Assessment) prescribes how to homogenize long-term records and continuously evaluate data quality for ongoing operations. We show: (1) how this framework has improved sonde precision from the 15-20% in the 1990s to 5% or better today with each ozonesonde record now traceable to a single standard; (2) examples of significant advances facilitated by increasingly rigorous ozone measurement standards.</jats:p>