Support Carbon Neutral Goal with a High-resolution Carbon Monitoring System in Beijing

China has committed to reach carbon neutral before 2060 in September 2020. To support the carbon neutral goal, carbon monitoring and inversions in greenhouse gases (GHG) emissions have become a hot topic in China. Here we introdue the Beijing-Tianjin-Hebei (JJJ) Carbon Monitoring System, established over the last seven years through a collaborative effort of 16 research institutions. The monitoring capability includes ground-based high-precision reference stations, a high-density network using low-cost sensors, GHG satellites, vertical profile samplers (AirCore), and mobile platforms. Observations using the network have shown CO₂ variations from diurnal to seasonal-interannual timescales, as well as dramatic on-road drop down signals during the COVID-19 pandemic lockdown. High-resolution modeling and data assimilation system at fine scale show deficiencies in global carbon emissions datasets at city scale. The atmospheric inversion found the total fossil fuel CO₂ emissions of Beijing to be 117 megatonne (Mt), which is much lower than the national-data-based inventories (152 MtCO₂). The results have been used in emissions assessment by national and local ecological and environmental monitoring agencies. Similar systems are now being developed in other Chinese cities.