Quantification des émissions de CO2 en Ile-de-France – CO2-MEGAPARIS

Atmospheric CO2 concentration has increasedby more than 30% since the pre-industrial era mainly due to industrial emissions and this increase is very likely at the root of the observed temperature rise of 0.6°C over the last century. Although we have good estimates of the CO2 fluxes on a global basis, regional information 10-500km) is needed if society is ever to manage or verify carbon emissions. New programs are needed to improve our understanding of meso-scale carbon fluxes, and to discriminate between the anthropogenic and biospheric sources which overlap very strongly in European countries. In this context, it is necessary to monitor the pollutant emissions originating from megalopolis such as Paris and its surburbs and the way they are spreading in the background atmosphere. Paris megacity is the third largest urban area in Europe.Nowadays, inventories (CITEPA) based on statistical information provide CO2 emissions from Ile de France, but no independent verification based on CO2 measurements has been performed. Atmospheric observations coupled to a meso-scale modelling framework can be used to provide such assessment, especially to detect the interannual and decadal trends which could result from regional management strategy. Finally, it is necessary to develop a stronger communication between scientists, society and stakeholders, in the aim of :1) get everyone conscious of his role in CO2 emissions ; and 2) give reliable material to regional political actors so that they can take proper decisions in matter if CO2 reduction policies. This proposal has a triple objective: 1) to assess by independant methods the inventories from CITEPA ; 2) to monitor the daily to monthly carbon emissions from the Parisian megalopolis at a very fine scale (up to 2x2 km2), and to study the propagation of the anthropogenic plumes to the neighbouring Centre region where about 40% of the winds come from the North/North-East sector i.e. from Paris agglomeration. ; and 3) to study how to establish and optimize the use of our scientific results on CO2 emissions by society and stakeholders. The proposed strategy for the quantification of CO2 emissions and their spread out of the Paris megacity relies on the development of a synergy between atmospheric observations for gaseous species and meteorological parameters (using ground-based, airborne and intensive campaigns measurements), CO2 biospheric fluxes observations, high resolution emission inventories and a mesoscale inverse modeling framework. Its originality is to assess the quantification of CO2 emissions by means of regional scale modeling and observation based approaches, in order to produce more reliable CO2 emissions budget for the studied regions that can be used for comparison with inventories. Both approaches rely on the use of the existing observation network from both regions, that will also be complemented by new measurements (in particular within AIRPARIF stations, and during intensive campaigns such as the MEGAPOLI wintertime one to which we will associate). This will develop a dense observing network for atmospheric CO2, meteorological parameters, CO2 emission tracers, and CO2 biospheric flux estimates. The inverse modeling framework will be set-up using the transport and biospheric flux modeling tools already in place at LSCE, and CITEPA inventories. The three observation based methods are : 1) the Radon method, based on Radon/CO2 correlation, that will provide integrated anthropogenic fluxes from the Paris urban area and in Centre region that will also be compared to inventories ; 2) an atmospheric boundary layer (ABL) budget method that will provide separate estimates of biospheric and anthropogenic fluxes for the Orléans forest region, located ~130 km south of the megacity, providing information on the propagation of the Ile de France emissions to the background atmosphere of the Orléans forest ; and 3) a 14CO2/CO correlation approach using as well a suite of pollution tracers from the EU/FP7/MEGAPOLI wintertime campaign, that will allow the precise discrimination of the main emission types and daily to weekly monitoring of fossil fuel CO2 emission sources in wintertime in Paris megacity. The modeling framework will be made of high resolution dedicated mesoscale models for atmospheric transport, especially in urban areas, and biospheric flux modelisation. Finally, the synergy will be put in place by comparing tracer concentrations, boundary layer height and CO2 fluxes produced by the different methods, assessing the advantages and the drawbacks of each of the approaches, and comparing the calculated fluxes issuing from this work to inventories. Eventually, the optimal development of the link we wish to establish between scientists, socio-economists, society and political actors will be studied in the framework of a « search conference » on the use of our results on CO2 emissions within the last months of the project.