1. Introduction

The TOAR database supports the Tropospheric Ozone Assessment Report activity (https://igacproject.org/activities/TOAR) through a uniform provision of harmonised long-term measurement series of ground-level (aka “surface”) ozone concentrations. TOAR has started its second phase (TOAR-II) in 2020 and we, the TOAR data team at Forschungszentrum Jülich, have developed a version 2 of the TOAR database to support TOAR-II. Unless explicitly noted, all information in this document applies to version 2 of the TOAR database and the associated web services. The TOAR-II activity is expected to end in 2024 and the majority of data gathering will take place in 2022. Version 1 of the database 1 will be operated in parallel until further notice. Note that there may be differences in the data series between versions 1 and 2 of the database due to updated information (e.g. new data submissions) or because of data license issues 2 .

Besides its main focus on ground-level ozone measurement series, the TOAR database also contains datasets of ozone precursors and of meteorological variables which can be used in the interpretation of the ozone concentrations and their changes in time. The data in the TOAR database is collected from several different sources (for details see TOAR Data Sources). Most of these data sources are public data archives and repositories. Some data stems from real-time or near-real time sources (OpenAQ initiative and the German Federal Environmental Agency, UBA). However, the TOAR database also functions as primary repository for some datasets which are not curated elsewhere.

Datasets (“series”) in the TOAR database are limited to ground-level measurements at stationary locations (“stations”). While the database contains some records where sampling occurred at higher altitudes (e.g. towers), vertical profile measurements or measurements from moving platforms (e.g. ships, aircraft) are out of scope for the TOAR database.

The TOAR-II activity pledges to adhere to the principles of COPDESS (https://copdess.org/) and the TOAR data infrastructure has been designed to support the emerging best practices for data sharing in the Earth and Space Sciences. The TOAR data team strives to operate its services including the TOAR database at the highest possible level of FAIRness (see https://www.force11.org/group/fairgroup/fairprinciples). A detailed assessment of the TOAR data service FAIRness can be found in Section 6 of this document.

In order to serve the database’s main purpose to provide “easily accessible, documented data on ozone mixing ratios, exposure and dose metrics at thousands of measurement sites around the world freely accessible for research on the global-scale impact of ozone on climate, human health and crop/ecosystem productivity”, all data in the TOAR database version 2 are openly accessible and can be used, modified and re-distributed under the Creative Commons (CC) BY license (i.e. “by attribution”; see https://creativecommons.org/licenses/by/4.0/) 2 .

Access to TOAR data is provided through one of three main channels:

Beginning with version 2, the first two channels allow direct access to the hourly-resolved ozone (precursor and meteorological) data. The third channel, the TOAR data publications, provide on the one hand access to harmonised data deposits of contributed data 5 and on the other hand pre-compiled aggregated datasets supporting the TOAR assessment papers.

If you are using or re-distributing data from the TOAR database, please adhere to the TOAR data use policy defined in Fig. 1.1 below and inform yourself about the terms and conditions of the CC-BY 4.0 license under which TOAR data are distributed.


Fig. 1.1 TOAR Data Use Policy



TOAR V1 is described in Schultz, M. G. et al. (2017) Tropospheric Ozone Assessment Report: Database and Metrics Data of Global Surface Ozone Observations, Elem Sci Anth, 5, p.58. DOI: http://doi.org/10.1525/elementa.244


Version 1 of the TOAR database operated under a different license model and contained embargoed data, which could not be distributed for research without explicit consent by the dataset providers. This “mixed-license” operation made it very difficult to further enhance the TOAR data services and we therefore adopted a fully open data policy for TOAR-II.


The version 1 REST API at https://join.fz-juelich.de/services/rest/surfacedata/ should now be accessed via https://toar-data.fz-juelich.de/api/v1/.


At the time of writing the GUI to access data from the TOAR database version 2 is still under development. Version 1 of the GUI, i.e. the JOIN web interface, can be reached at https://toar-data.fz-juelich.de/gui/v1/


The primary data provided by individual research teams or air quality agencies. B2SHARE data publications include a DOI which shall be used to properly cite such datasets.