城市及区域尺度碳同化反演研究进展

RESEARCH PROGRESS IN URBAN AND REGIONAL-SCALE ATMOSPHERIC INVERSIONS OF CARBON SOURCES AND SINKS

双碳战略背景下,对碳源、汇的准确估算提出了迫切需求。尽管"自上而下"碳同化反演理论严谨,但从大气浓度变化反演碳源汇,长期以来是一个具有挑战性的科学问题。以往基于卫星和地面监测的大气反演,已在全球尺度上提升了陆地和海洋碳源汇的认识。然而,城市和区域尺度碳源汇估算仍有很大的不确定性。一方面,在区域尺度,我国陆地生态系统碳源汇反演大多采用全球大气传输模式,在月和周时间尺度上同化,有限的观测资料和模式分辨率导致反演的不确定性很大。基于中尺度大气传输模式的区域碳同化,通过提升碳源汇估算的时空分辨率,改进陆地碳源汇反演水平。另一方面,在城市尺度,城市是人为碳排放的主要来源,基于能源消耗统计数据的"自下而上"清单法不确定性大且更新慢。通过碳同化反演,可获得客观及时的碳排放数据,实现与"自下而上"清单的相互校验。总体上,近年来城市和区域尺度碳同化取得了很大进展,未来亟须进一步降低模式和观测不确定性的影响,开展自然源和人为源的精准反演,为双碳目标提供科学支撑。

Achieving carbon peak and carbon neutrality is a major strategy made by China,which puts forward an urgent need for accurate estimation of carbon sources and sinks.More and more concerns are focused on top-down approaches,which estimate the CO2 exchanges of the Earth’s surface with atmosphere to ensure the objectivity,rationality and accuracy of carbon data.Although the theory of top-down inversion is rigorous,the inversion of carbon source and sink from atmospheric concentration variations turns out to be a challenging scientific problem for a long time.Based on space-borne and ground-based measurements,previous atmospheric inversions have improved the understanding of global terrestrial and ocean carbon fluxes.However,there are still significant uncertainties in the estimation of carbon fluxes at urban and regional scales.On the one hand,at the regional scale,the atmospheric inversion of China’s terrestrial biosphere carbon sources and sinks are used as a reference.Most of China’s carbon sink inversion research adopts global atmospheric transport models to assimilate natural fluxes,which quantifies the biosphere carbon budget with a relatively coarse spatial resolution and long timescale from a weekly or monthly perspective.The limitations in observations and model errors lead to great uncertainty in the inversions,and there is considerable controversy among previous top-down results.Based on the mesoscale atmospheric transport models,several regional carbon assimilation schemes were found to help improve the spatiotemporal resolution of carbon fluxes estimation and reduce the bias in atmospheric inversion.At the urban scale,cities are the main sources of CO2 anthropogenic emissions.The bottom-up approach,taking inventory as an example,has some disadvantages on account of the uncertainties and temporal hysteresis in statistics of energy consumption data.Through carbon assimilation techniques,carbon emissions can be estimated more objectively and timely.Moreover,implementing cross-validation of top-down and bottom-up estimates is beneficial to the credibility of carbon data.In general,great progress has been made in carbon data assimilation at the urban and regional scales during recent decades.In the future,it is urgent to reduce the impact of model and observation uncertainties,to carry out accurate inversions from terrestrial and anthropogenic aspects,which will form an important scientific and practical basis for investigating the regional carbon cycle.