Atmospheric CO2 variability, sources and sinks in the Aix-Marseille-Provence metropolis area, France

The Aix-Marseille-Provence metropolis (AMPm), located on the south-east coast of France, is the second most populated urbanized area of the country. Characterized by a Mediterranean climate, this area is classified as a hot-spot regarding climate change. Its west part is strongly industrialized. The AMPm benefits of a high resolved greenhouse gas emissions inventory which serves as a reference to stakeholders for defining AMPm CO2 emissions mitigation strategies. However this inventory is characterized by large uncertainties and which requires independent assessments. Atmospheric top-down approaches can provide such information. In the framework of the ANR COoL-AMmetropolis project and of the national ICOS-France observation network, a regional greenhouse gas monitoring network based on five Cavity Ring Down Spectrometry analyzers was deployed in and around the AMPm between 2014 and 2021. The stations were also equiped with meteorological sensors. An 532nm-backscattering aerosols Lidar was set-up on one of the sites to infer the boundary layer height. The regional variability of atmospheric CO2 was analyzed from these datasets to assess the role of local sources and sinks, of meteorological features such as breezes and of boundary layer dynamical processes. In addition, two intensive field campaigns were carried out during which carbon isotopes in CO2 and atmospheric CO2 co-emitted species were measured within AMPm urban and industrial CO2 plumes. The isotopic analysis of 14C and 13C in CO2, as well as CO2 correlations with NOx, CO, black carbon and SO2, shows that : 1/ emissions from fossil fuel combustion processes - mostly from traffic, building, industrial and maritime activities - play a major role on the CO2 local urban and industrial plumes ; and 2/ modern sources such as wood burning may account for a larger part in the total AMPm CO2 emissions than assessed by the local inventory.