Observed decreases in on-road CO2 concentrations in Beijing during COVID-19 restrictions Di Liu1, Wanqi Sun2, Ning Zeng3,4, , Pengfei Han1*, Bo Yao2, *, Zhiqiang Liu1, Pucai Wang5, Ke Zheng1, Han Mei1, Qixiang Cai1 5 1Laboratory of Numerical Modeling for Atmospheric Sciences & Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences 2Meteorological Observation Centre, China Meteorological Administration, Beijing, China 3Department of Atmospheric and Oceanic Science, University of Maryland, USA 10 4Earth System Science Interdisciplinary Center, University of Maryland, USA 5Laboratory for Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences * Correspondence to: Pengfei Han (
[email protected]); Bo Yao (
[email protected]) 15 Abstract: 带格式的: 字体: (默认) 宋体, (中文) 宋体, 小四 To prevent the spread of the COVID-19 epidemic, restrictions such as “lockdowns”, were conducted globally, which led to a 带格式的: 正文, 段落间距段前: 0 磅, 段后: 0 磅 significant reduction in fossil fuel emissions, especially in urban regionsareas. However, CO2 concentrations in urban 20 regions areas are affected by many factors, such as weather, biological sinks and background CO2 fluctuations. Thus, it is 带格式的: 下标 difficult to directly observe the CO2 reductions in CO2 concentrations with from sparse ground observations. Here, we focus on urban ground transportation emissions, which were dramatically affected by the prohibitionsrestrictions, to determine the reduction signals. We conducted six