The unified database of ozonesounding profiles was obtained through the merging of three existing ozonesounding datasets, provided by the Southern Hemisphere Additional OZonesondes (SHADOZ), the Network for the Detection of Atmospheric Composition Change (NDACC), and the World Ozone and Ultraviolet Radiation Data Centre (WOUDC). Only a few variables of interest, shown in the Table, were considered to build the unified dataset due to the different formats and amounts of data and metadata provided by each network, despite data often referring to the measurements provided to different initiatives. Standard name Description Unit idstation The name of the station. N.A. lat Latitude of station. deg lon Longitude of station. deg date_of_observation Date when the ozonesonde was launched (in format yyyy-mm-dd hh:mm:ss with time zone). N.A. press Atmospheric pressure of each level in Pascals. Pa temp Air temperature in degrees Kelvin. K rh Relative humidity in 1. 1 gps_lat Observation latitude (during the flight). deg gps_lon Observation longitude (during the flight). deg gps_alt Height of sensor above local ground or sea surface. Positive values for above surface (e.g., sondes), negative for below (e.g., xbt). For visual observations, the height of the visual observing platform. m (a. s. l.) o3_partial_pressure The level partial pressure of ozone in Pascals. Pa o3_concentration The level mixing ratio of ozone in ppmv. ppmv o3_partial_pressure_total_uncertainty Total uncertainty in the calculation of the ozone partial pressure as a composite of the individual uncertainty contribution. Uncertainties due to systematic bias are assumed as random and follow a random normal distribution. The uncertainty calculation also accounts for the increased uncertainty incurred by homogenizing the data record. Pa network Source network of the profile. N.A. type Station classification flag. N.A. Furthermore, an algorithm was implemented able to merge the different datasets by handling their different features and duplicated profiles. The selection criteria are summarized below: In case of a single profile for a day (no duplicates), this profile will be saved in the database; In case of duplicates, the profile selection is driven by the dataset maturity and by the availability of measurement uncertainties on the ozone concentration profiles. The uncertainties are provided mainly in the SHADOZ database and for some locations also in the NDACC database. WOUDC, on the other hand, does not provide any uncertainty estimates; Discarded profiles are eventually used to densify the vertical sampling if they provide measurements at different pressure levels not available in the selected profiles.