Steinbrecht, W., Kubistin, D., Plass-Dülmer, C., Davies, J., Tarasick, D. W., von der Gathen, P., et al. incl Palm, M., Notholt, J., 2021. COVID-19 crisis reduces free tropospheric ozone across the Northern Hemisphere. Geophys. Res. Lett. 48, e2020GL091987. https://doi.org/10.1029/2020GL091987