Tropospheric Ozone Assessment Report (TOAR): Global metrics for climate change, human health and crop/ecosystem research


Join us for the TOAR-II Quickstart Event, September 16, 2020

The second phase of the Tropospheric Ozone Assessment Report (TOAR-II) is beginning with an open call to the research community to build the assessment and coordinate new studies on ozone’s global distribution and trends, as well as impacts on human health, vegetation and climate.  To learn more about, or to get involved with this grass roots effort please attend the TOAR-II Quickstart Event on September 16, 2020. This 90-minute virtual event will include a series of short presentations from the TOAR-II Steering Committee covering the scope and goals of the Activity, followed by a Q&A session.

Please register for the TOAR-II Quickstart Event on Sep 16, 2020 (12:00-13:30 UTC) at:

To join the TOAR-II email list, sign-up here




TOAR has completed its first phase and TOAR-II has been approved by the IGAC Scientific Steering Committee. A new Steering Committee will develop a work plan and roadmap for TOAR-II activities. Stay tuned for announcements coming soon!


TOAR’s mission is to provide the research community with an up-to-date scientific assessment of tropospheric ozone’s global distribution and trends from the surface to the tropopause. This includes the production of tropospheric ozone assessment reports based on the peer-reviewed literature and new analyses as well as the provision of easily accessible, documented data on ozone mixing ratios, exposure and dose metrics at thousands of measurement sites around the world, and links to quality assessed data sources of free tropospheric ozone at the TOAR data portal. All TOAR data are freely accessible for research on the global-scale impact of ozone on climate, human health and crop/ecosystem productivity.


TOAR is a science effort initiated by IGAC, and developed by an international team of more than 200 experts from over 35 countries. TOAR receives financial and logistical support from IGAC, Forschungszentrum Jülich, the US National Oceanic and Atmospheric Administration, and the World Meteorological Organization (an agency of the United Nations).

Achievements, plans, and ongoing work:

As of February 2020, TOAR entered its second phase and is now preparing to launch an updated tropospheric ozone assessment. For details, see TOAR Phase-II . The first phase of TOAR has achieved its two main objectives, namely a set of 8 peer-reviewed publications (Elementa special feature), and a web-accessible database of surface ozone observations ( For details, see TOAR Phase-I.

TOAR data and tools:


Tropospheric Ozone Assessment Report: Tropospheric ozone from 1877 to 2016, observed levels, trends and uncertainties. Tarasick, D., Galbally, I.E., Cooper, O.R., Schultz, M.G., Ancellet, G., Leblanc, T., Wallington, T.J., Ziemke, J., Liu, X., Steinbacher, M., Staehelin, J., Vigouroux, C., Hannigan, J.W., García, O., Foret, G., Zanis, P., Weatherhead, E., Petropavlovskikh, I., Worden, H., Osman, M., Liu, J., Chang, K.-L., Gaudel, A., Lin, M., Granados-Muñoz, M., Thompson, A.M., Oltmans, S.J., Cuesta, J., Dufour, G., Thouret, V., Hassler, B., Trickl, T. and Neu, J.L., 2019. Tropospheric Ozone Assessment Report: Tropospheric ozone from 1877 to 2016, observed levels, trends and uncertainties. Elem Sci Anth, 7(1), p.39. DOI : 10.1525/elementa.376.

Tropospheric Ozone Assessment Report: Present-day tropospheric ozone distribution and trends relevant to vegetation. Mills G, Pleijel H, Malley CS, Sinha B, Cooper OR, Schultz MG, Neufeld HS, Simpson D, Sharps K,  Feng Z,  Gerosa G,  Harmens H, Kobayashi K,  Saxena P,  Paoletti E,  Sinha V, Xu X,. Elem Sci Anth. 2018;6(1):47. DOI: 10.1525/elementa.302.

Tropospheric Ozone Assessment Report: Present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation. Gaudel, A., Cooper, O.R., Ancellet, G., Barret, B., Boynard, A., Burrows, J.P., Clerbaux, C., Coheur, P.-F., Cuesta, J., Cuevas, E., Doniki, S., Dufour, G., Ebojie, F., Foret, G., Garcia, O., Granados Muños, M.J., Hannigan, J.W., Hase, F., Huang, G., Hassler, B., Hurtmans, D., Jaffe, D., Jones, N., Kalabokas, P., Kerridge, B., Kulawik, S.S., Latter, B., Leblanc, T., Le Flochmoën, E., Lin, W., Liu, J., Liu, X., Mahieu, E., McClure-Begley, A., Neu, J.L., Osman, M., Palm, M., Petetin, H., Petropavlovskikh, I., Querel, R., Rahpoe, N., Rozanov, A., Schultz, M.G., Schwab, J., Siddans, R., Smale, D., Steinbacher, M., Tanimoto, H., Tarasick, D.W., Thouret, V., Thompson, A.M., Trickl, T., Weatherhead, E., Wespes, C., Worden, H.M., Vigouroux, C., Xu, X., Zeng, G. and Ziemke, J., 2018. Elem Sci Anth, 6(1), p.39. DOI: 10.1525/elementa.291.

Tropospheric ozone assessment report: Global ozone metrics for climate change, human health, and crop/ecosystem research. Lefohn, AS, Malley, CS, Smith, L, Wells, B, Hazucha, M, Simon, H, Naik, V, Mills, G, Schultz, MG, Paoletti, E, De Marco, A, Xu, X, Zhang, L, Wang, T, Neufeld, HS, Musselman, RC, Tarasick, D, Brauer, M, Feng, Z, Tang, H, Kobayashi, K, Sicard, P, Solberg, S and Gerosa, G 2018. Elem Sci Anth, 6: 28. DOI: 10.1525/elementa.279. 

Tropospheric Ozone Assessment Report: Present-day ozone distribution and trends relevant to human health. Fleming, Z.L., Doherty, R.M., von Schneidemesser, E., Malley, C.S., Cooper, O.R., Pinto, J.P., Colette, A., Xu, X., Simpson, D., Schultz, M.G., Lefohn, A.S., Hamad, S., Moolla, R., Solberg, S. and Feng, Z., 2018. Elem Sci Anth, 6(1), p.12. DOI: 10.1525/elementa.73.

Tropospheric Ozone Assessment Report: Assessment of global-scale model performance for global and regional ozone distributions, variability, and trends. Young, P.J., Naik, V., Fiore, A.M., Gaudel, A., Guo, J., Lin, M.Y., Neu, J.L., Parrish, D.D., Rieder, H.E., Schnell, J.L., Tilmes, S., Wild, O., Zhang, L., Ziemke, J.R., Brandt, J., Delcloo, A., Doherty, R.M., Geels, C., Hegglin, M.I., Hu, L., Im, U., Kumar, R., Luhar, A., Murray, L., Plummer, D., Rodriguez, J., Saiz-Lopez, A., Schultz, M.G., Woodhouse, M.T. and Zeng, G., 2018. Elem Sci Anth, 6(1), p.10. DOI: 10.1525/elementa.265.

Tropospheric Ozone Assessment Report: Database and Metrics Data of Global Surface Ozone Observations. Schultz, M.G., Schröder, S., Lyapina, O., Cooper, O., Galbally, I., Petropavlovskikh, I., von Schneidemesser, E., Tanimoto, H., Elshorbany, Y., Naja, M., Seguel, R., Dauert, U., Eckhardt, P., Feigenspahn, S., Fiebig, M., Hjellbrekke, A.-G., Hong, Y.-D., Christian Kjeld, P., Koide, H., Lear, G., Tarasick, D., Ueno, M., Wallasch, M., Baumgardner, D., Chuang, M.-T., Gillett, R., Lee, M., Molloy, S., Moolla, R., Wang, T., Sharps, K., Adame, J.A., Ancellet, G., Apadula, F., Artaxo, P., Barlasina, M., Bogucka, M., Bonasoni, P., Chang, L., Colomb, A., Cuevas, E., Cupeiro, M., Degorska, A., Ding, A., Fröhlich, M., Frolova, M., Gadhavi, H., Gheusi, F., Gilge, S., Gonzalez, M.Y., Gros, V., Hamad, S.H., Helmig, D., Henriques, D., Hermansen, O., Holla, R., Huber, J., Im, U., Jaffe, D.A., Komala, N., Kubistin, D., Lam, K.-S., Laurila, T., Lee, H., Levy, I., Mazzoleni, C., Mazzoleni, L., McClure-Begley, A., Mohamad, M., Murovic, M., Navarro-Comas, M., Nicodim, F., Parrish, D., Read, K.A., Reid, N., Ries, L., Saxena, P., Schwab, J.J., Scorgie, Y., Senik, I., Simmonds, P., Sinha, V., Skorokhod, A., Spain, G., Spangl, W., Spoor, R., Springston, S.R., Steer, K., Steinbacher, M., Suharguniyawan, E., Torre, P., Trickl, T., Weili, L., Weller, R., Xu, X., Xue, L. and Zhiqiang, M., 2017.  Elem Sci Anth, 5, p.58. DOI: 10.1525/elementa.244.

Regional trend analysis of surface ozone observations from monitoring networks in eastern North America, Europe and East Asia. Chang K-L, Petropavlovskikh I, Cooper OR, Schultz MG, Wang T. Elem Sci Anth. 2017;5:50. DOI: 10.1525/elementa.243.