Anomalies of O3, CO, C2H2, H2CO, and C2H6 detected with multiple ground-based Fourier-transform infrared spectrometers and assessed with model simulation in 2020: COVID-19 lockdowns versus natural variability

Anomalies of tropospheric columns ozone (O3), carbon monoxide (CO), acetylene (C2H2), formaldehyde (H2CO), and ethane (C2H6) are quantified during the 2020 stringent COVID-19 world-wide lockdown using multiple ground-based Fourier-transform infrared spectrometers covering urban remote conditions. We applied an exponential smoothing forecasting approach to data sets estimate business-as-usual values for 2020, which then contrasted with actual observations. The Community Atmosphere Model chemistry (CAM-chem) is used simulate same gases lockdown-adjusted emissions. role meteorology, or natural variability, assessed additional CAM-chem simulations. column O3 declined between March May most sites a mean decrease 9.2% ± 4.7%. Simulations reproduce these anomalies, especially under background conditions where variability explains up 80% decline in Northern Hemisphere. While show reduction 1% 12% CO, do not significant change. Overall, simulations capture magnitude anomalies many cases lockdowns have opposite effects. further long-term record Measurements Pollution Troposphere (MOPITT) satellite instrument global CO. Reductions CO vary highly across regions but North America Europe registered lower 2020. absence April May, concomitant reductions anthropogenic emissions, explained by negative anomaly hydroxyl radical (OH) found CAM-chem. implications findings discussed methane (CH4), shows positive lifetime period. fossil fuel combustion by-product tracer C2H2 drop 13.6% 8.3% Hemisphere due emissions some exacerbated variability. For influence there C2H6. main cause may be related H2CO all precursors.