A high-resolution simulation of CO2 at 1×1 km horizontal resolution using the Weather Research and Forecasting Greenhouse gas (WRF-GHG) model was conducted, focusing on the Kanto region in Japan. The WRF-GHG simulations were performed using different anthropogenic emission inventories: EAGrid (Japan, 1 km), EDGAR (0.1o), and EDGAR-downscaled (0.01o). Our analysis showed that the simulations using EAGrid better captured the diurnal variability in observed CO2 compared to EDGAR and EDGAR-downscaled emissions at two continuous monitoring sites. The 1×1 km simulation performed better in simulating CO2 variability observed in surface sites (hourly) and aircraft observations, compared to the 27×27 km simulations. We compared the vertical profile distribution of CO2 and found that all the simulations performed similarly. During February (May), the anthropogenic (land biosphere) fluxes were the primary contributor to the vertical distribution of CO2 up to an altitude of 3200 m (4500 m), beyond which long-range transport influenced by lateral boundary conditions from Eurasia played a greater role. The sensitivity analysis of boundary conditions showed a systematic bias (~ 4 ppm) persisting above 3200 m altitude when fixed (a constant value) boundary conditions are applied, as compared to the simulation with boundary conditions from a global model. We also compared the WRF-GHG simulated column-averaged XCO2 from Orbiting Carbon Observatory-2 (OCO-2) satellite and found a statistically significant spatial correlation (r=0.47) in February. However, we found a weaker spatial correlation (0.17) in May, which could be caused due to under-representation of intense land biosphere activity in WRF-GHG.

Efforts to slow the transmission of COVID-19 led to rapid, global ancillary reductions in air pollutant emissions. Here, we quantify the resulting decreases in global NOx emissions and their consequent impact on the production of global tropospheric ozone using a multi-constituent data assimilation system. Total anthropogenic NOx emissions were reduced by at least 15% globally and 18-25% for Europe, North America, and the Middle East in April and May 2020. The efficacy of these reductions in altering ozone concentrations varied substantially in both space and time, with differences driven by local meteorology and chemical production efficiency. Globally, the total tropospheric ozone burden dropped by about 6 TgO 3 (∼2%) in May-June 2020, largely due to emission reductions in Asia and the Americas. Our results show a clear and global atmospheric imprint from COVID-19 mitigation, which altered the atmospheric oxidative capacity, climate radiative forcing, and human health.