Abstract
Abstract. Accurate simulation of the spatial and temporal variability of tracer mixing ratios over urban areas is a challenging and interesting task needed to be performed in order to utilise CO2 measurements in an atmospheric inverse framework and to better estimate regional CO2 fluxes. This study investigates the ability of a high-resolution model to simulate meteorological and CO2 fields around Paris agglomeration during the March field campaign of the CO2-MEGAPARIS project. The mesoscale atmospheric model Meso-NH, running at 2 km horizontal resolution, is coupled with the Town Energy Balance (TEB) urban canopy scheme and with the Interactions between Soil, Biosphere and Atmosphere CO2-reactive (ISBA-A-gs) surface scheme, allowing a full interaction of CO2 modelling between the surface and the atmosphere. Statistical scores show a good representation of the urban heat island (UHI) with stronger urban–rural contrasts on temperature at night than during the day by up to 7 °C. Boundary layer heights (BLH) have been evaluated on urban, suburban and rural sites during the campaign, and also on a suburban site over 1 yr. The diurnal cycles of the BLH are well captured, especially the onset time of the BLH increase and its growth rate in the morning, which are essential for tall tower CO2 observatories. The main discrepancy is a small negative bias over urban and suburban sites during nighttime (respectively 45 m and 5 m), leading to a few overestimations of nocturnal CO2 mixing ratios at suburban sites and a bias of +5 ppm. The diurnal CO2 cycle is generally well captured for all the sites. At the Eiffel tower, the observed spikes of CO2 maxima occur every morning exactly at the time at which the atmospheric boundary layer (ABL) growth reaches the measurement height. At suburban ground stations, CO2 measurements exhibit maxima at the beginning and at the end of each night, when the ABL is fully contracted, with a strong spatio-temporal variability. A sensitivity test without urban parameterisation removes the UHI and underpredicts nighttime BLH over urban and suburban sites, leading to large overestimation of nocturnal CO2 mixing ratio at the suburban sites (bias of +17 ppm). The agreement between observation and prediction for BLH and CO2 concentrations and urban–rural increments, both day and night, demonstrates the potential of using the urban mesoscale system in the context of inverse modelling
Highlights
Earth System SciencesIt has been widely reported that atmospheric CO2 concentration has increased by more than 30 % since the pre-industrial era mainly due to human activities and this increase is very likely at over the the last root of century t(hFeOoroscbteserearevtneadl.S,te2mc00ipe7e)rn.atAculretehoriusgehowf e0.h6a◦vCe good estimates of the CO2 fluxes on a global basis, and have a relatively well-established observation network to detect the large-scale trends, regional information (10–500 km) is needed if society is ever to manage or verify carbon emissions (Dolman et al, 2006).SWoelimdusEt aimrpthrove our understanding of regional variations in sources and sinks of CO2 to identify possible sequestration or emission managementPublished by Copernicus Publications on behalf of the European Geosciences Union.The Cryosphere options
As JUSS is close to EIF, observed and predicted Boundary layer heights (BLH) evolutions at JUSS are used to help in analysing CO2 observations and predictions at EIF (Fig. 11)
In order to better understand the effects that mesoscale transport has on atmospheric CO2 distributions in urban and suburban areas, the mesoscale atmospheric model Meso-NH coupled with the Town Energy balance (TEB) urban canopy scheme and with the Interactions between Soil, Biosphere and Atmosphere CO2-reactive (ISBA-A-gs) surface scheme was run for the period from 21 March to 26 March in 2011 covering the campaign of CO2-MEGAPARIS project
Summary
Earth System SciencesIt has been widely reported that atmospheric CO2 concentration has increased by more than 30 % since the pre-industrial era mainly due to human activities and this increase is very likely at over the the last root of century t(hFeOoroscbteserearevtneadl.S,te2mc00ipe7e)rn.atAculretehoriusgehowf e0.h6a◦vCe good estimates of the CO2 fluxes on a global basis, and have a relatively well-established observation network to detect the large-scale trends, regional information (10–500 km) is needed if society is ever to manage or verify carbon emissions (Dolman et al, 2006).SWoelimdusEt aimrpthrove our understanding of regional variations in sources and sinks of CO2 to identify possible sequestration or emission managementThe Cryosphere options. It is necessary to discriminate between the anthropogenic and biospheric sources which overlap very strongly in European countries In this context, the project CO2MEGAPARIS aims at the quantification of the CO2 emissions of the megacity Paris and the simulation and assessment of the anthropogenic CO2 plume over the Ile-de-France province (corresponding to the Paris administrative region) (Xueref-Remy et al, 2012). With 12 million of inhabitants, Paris is the third largest megacity of Europe (after London and Moscow), and is estimated to emit about 14 % of national emissions. It is an ideal test location due to its relatively well defined boundaries and the lack of other major CO2 emitters in its immediate vicinity. The former experiment ESQUIF (Vautard et al, 2003) gave a fair understanding of the atmospheric dynamics in this area and the impact on air quality
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