Dynamics of urban carbon emissions: A comparative analysis of pre- and post-lockdown through eddy covariance...

Urban areas are the major anthropogenic source of atmospheric CO₂, thus making long-term and continuous observations of their carbon emission dynamics extremely important. The COVID-19 lockdown served as a natural experiment that provided a unique opportunity to analyse the contribution of human activities to CO₂ emissions from urban areas. In 2020, Beijing experienced COVID-19 confinement with different levels of restrictions on social mobility and economic activity, resulting in reductions in CO₂ emissions. To investigate the response mechanisms of CO₂ flux to restriction measures, we analysed CO₂ flux data obtained using the eddy covariance technique from 2015 to 2020, and compared CO₂ flux during the COVID-19 confinement period in 2020 with the preceding years (2015-2019) and across various levels of confinement. The results showed that: (1) the annual CO₂ flux was 2.1 ± 0.2 kg C/(m²·yr) in 2020, which showed a significant reduction of 31.8 % compared to the adjacent 2019; (2) the reduction in CO₂ flux was closely related to the level of restrictions on human activities; (3) most reductions occurred during the morning (85.7 %) and evening (32.7 %) peak traffic times, indicating that commuting-related transportation is a primary contributor to urban CO₂ emissions. It is suggested that measures that reduce transportation-related CO₂ sources should be considered as priorities for reducing urban CO₂ emissions. The dynamic variation of urban CO₂ flux captured by the eddy covariance technology is conductive to strengthening the supervision of the implementation of urban carbon emission reduction policies, promoting the achievement of dual carbon goals.