This study estimates the influence of anthropogenic emission reductions on nitrogen dioxide (NO_2) and ozone (O_3) concentration changes during the COVID-19 pandemic period using in-situ surface and Sentinel-5p (TROPOMI) satellite column measurements and GEOS-Chem model simulations. We show that, as a result of reductions in anthropogenic emission in eight German metropolitan cities, meteorology corrected mean in-situ (\& column) NO_2(2020,corr) concentrations decreased by 23 ± 4.7 % (& 16.4 ± 7.2 %) between March 21 and June 30, 2020, whereas meteorology corrected mean in-situ O_3(2020,corr) concentration increased by 4 ± 8.8 % between March 21 and May 31, 2020, and decreased by 3 ± 8.7 % in June 2020, compared to 2019 (uncertainty represents the 1 σ of mean changes of eight metropolitan cities). The impacts of meteorology on in-situ and TROPOMI NO_2 concentration changes during the lockdown compared to 2019 are relatively small (+0.4 % and -0.6 %, respectively), while those on in-situ O_3 concentration changes are more significant (+3.6 % and -13.5 % for March 21 to May 31, 2020 and June 2020, respectively). A NO_X saturated ozone production regime in German metropolitan cities in March to May explains the increased O_3(2020,corr) concentration in response to the decreased NO_2(2020,corr) concentration. This implies that future reductions in NO_X emissions are likely to increase ozone pollution in these cities if appropriate mitigation measures are not implemented. TROPOMI NO_2(2020,corr) concentrations decreased nationwide during the stricter lockdown period, except for North-West Germany, which can be attributed to enhanced NO_X emissions from agricultural soils.