Atmospheric concentration measurements are used to adjust the daily to monthly budget of fossil fuel CO2 emissions of the Paris urban area from the prior estimates established by the Airparif local ...air quality agency. Five atmospheric monitoring sites are available, including one at the top of the Eiffel Tower. The atmospheric inversion is based on a Bayesian approach, and relies on an atmospheric transport model with a spatial resolution of 2 km with boundary conditions from a global coarse grid transport model. The inversion adjusts prior knowledge about the anthropogenic and biogenic CO2 fluxes from the Airparif inventory and an ecosystem model, respectively, with corrections at a temporal resolution of 6 h, while keeping the spatial distribution from the emission inventory. These corrections are based on assumptions regarding the temporal autocorrelation of prior emissions uncertainties within the daily cycle, and from day to day. The comparison of the measurements against the atmospheric transport simulation driven by the a priori CO2 surface fluxes shows significant differences upwind of the Paris urban area, which suggests a large and uncertain contribution from distant sources and sinks to the CO2 concentration variability. This contribution advocates that the inversion should aim at minimising model-data misfits in upwind-downwind gradients rather than misfits in mole fractions at individual sites. Another conclusion of the direct model-measurement comparison is that the CO2 variability at the top of the Eiffel Tower is large and poorly represented by the model for most wind speeds and directions. The model's inability to reproduce the CO2 variability at the heart of the city makes such measurements ill-suited for the inversion. This and the need to constrain the budgets for the whole city suggests the assimilation of upwind-downwind mole fraction gradients between sites at the edge of the urban area only. The inversion significantly improves the agreement between measured and modelled concentration gradients. Realistic emissions are retrieved for two 30-day periods and suggest a significant overestimate by the AirParif inventory. Similar inversions over longer periods are necessary for a proper evaluation of the optimised CO2 emissions against independent data.
While previous research helped to identify and prioritize the sources of error in air-quality modeling due to anthropogenic emissions and spatial scale effects, our knowledge is limited on how these ...uncertainties affect climate-forced air-quality assessments. Using as reference a 10-year model simulation over the greater Paris (France) area at 4 km resolution and anthropogenic emissions from a 1 km resolution bottom-up inventory, through several tests we estimate the sensitivity of modeled ozone and PM2.5 concentrations to different potentially influential factors with a particular interest over the urban areas. These factors include the model horizontal and vertical resolution, the meteorological input from a climate model and its resolution, the use of a top-down emission inventory, the resolution of the emissions input and the post-processing coefficients used to derive the temporal, vertical and chemical split of emissions. We show that urban ozone displays moderate sensitivity to the resolution of emissions (~ 8 %), the post-processing method (6.5 %) and the horizontal resolution of the air-quality model (~ 5 %), while annual PM2.5 levels are particularly sensitive to changes in their primary emissions (~ 32 %) and the resolution of the emission inventory (~ 24 %). The air-quality model horizontal and vertical resolution have little effect on model predictions for the specific study domain. In the case of modeled ozone concentrations, the implementation of refined input data results in a consistent decrease (from 2.5 up to 8.3 %), mainly due to inhibition of the titration rate by nitrogen oxides. Such consistency is not observed for PM2.5. In contrast this consistency is not observed for PM2.5. In addition we use the results of these sensitivities to explain and quantify the discrepancy between a coarse (~ 50 km) and a fine (4 km) resolution simulation over the urban area. We show that the ozone bias of the coarse run (+9 ppb) is reduced by ~ 40 % by adopting a higher resolution emission inventory, by 25 % by using a post-processing technique based on the local inventory (same improvement is obtained by increasing model horizontal resolution) and by 10 % by adopting the annual emission totals of the local inventory. The bias of PM2.5 concentrations follows a more complex pattern, with the positive values associated with the coarse run (+3.6 mu g m-3), increasing or decreasing depending on the type of the refinement. We conclude that in the case of fine particles, the coarse simulation cannot selectively incorporate local-scale features in order to reduce its error.
Measurements of CO2, CO, NOx and selected Volatile Organic Compounds (VOCs) mole fractions were performed continuously during a 10-day period in the Guy Môquet tunnel in Thiais, a peri-urban area ...about 15 km south of the centre of Paris, between 28 September and 8 October 2012. This data set is used here to identify the characteristics of traffic-emitted CO2 by evaluating its ratios to co-emitted species for the first time in the Paris region. High coefficients of determination (r2 > 0.7) are observed between CO2 and certain compounds that are characteristic of the traffic source (CO, NOx, benzene, xylenes and acetylene). Weak correlations (r2 < 0.2) are found with species such as propane, n-butane and i-butane that are associated with fuel evaporation, an insignificant source for CO2. To better characterise the traffic signal we focus only on species that are well-correlated with CO2 and on rush-hour periods characterised by the highest traffic-related mole fractions. From those mole fractions we remove the nighttime-average weekday mole fraction obtained for each species that we infer to be the most appropriate background signal for our study. Then we calculate observed Δspecies / ΔCO2 ratios, which we compare with the ones provided by the 2010 bottom–up high-resolved regional emission inventory from Airparif (the association in charge of monitoring the air quality in Île-de-France), focusing on local emission data for the specific road of the tunnel. We find an excellent agreement (2%) between the local inventory emission CO / CO2 ratio and our observed ΔCO / ΔCO2 ratio. Former tunnel experiments carried out elsewhere in the world provided observed ΔCO / ΔCO2 ratios that differ from 49 to 592% to ours. This variability can be related to technological improvement of vehicles, differences in driving conditions, and fleet composition. We also find a satisfactory agreement with the Airparif inventory for n-propylbenzene, n-pentane and xylenes to CO2 ratios. For most of the other species, the ratios obtained from the local emission inventory overestimate the observed ratios to CO2 by 34 to more than 300%. However, the emission ratios of NOx, o-xylene and i-pentane are underestimated by 30 to 79%. One main cause of such high differences between the inventory and our observations is likely the obsolete feature of the VOCs speciation matrix of the inventory that has not been updated since 1998, although law regulations on some VOCs have occurred since that time. Our study bears important consequences, discussed in the conclusion, for the characterisation of the urban CO2 plume and for atmospheric inverse modelling of urban CO2 emissions.
Simulations with the chemistry transport model CHIMERE are compared to measurements performed during the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate ...effects, and Integrated tools for assessment and mitigation) summer campaign in the Greater Paris region in July 2009. The volatility-basis-set approach (VBS) is implemented into this model, taking into account the volatility of primary organic aerosol (POA) and the chemical aging of semi-volatile organic species. Organic aerosol is the main focus and is simulated with three different configurations with a modified treatment of POA volatility and modified secondary organic aerosol (SOA) formation schemes. In addition, two types of emission inventories are used as model input in order to test the uncertainty related to the emissions. Predictions of basic meteorological parameters and primary and secondary pollutant concentrations are evaluated, and four pollution regimes are defined according to the air mass origin. Primary pollutants are generally overestimated, while ozone is consistent with observations. Sulfate is generally overestimated, while ammonium and nitrate levels are well simulated with the refined emission data set. As expected, the simulation with non-volatile POA and a single-step SOA formation mechanism largely overestimates POA and underestimates SOA. Simulation of organic aerosol with the VBS approach taking into account the aging of semi-volatile organic compounds (SVOC) shows the best correlation with measurements. High-concentration events observed mostly after long-range transport are well reproduced by the model. Depending on the emission inventory used, simulated POA levels are either reasonable or underestimated, while SOA levels tend to be overestimated. Several uncertainties related to the VBS scheme (POA volatility, SOA yields, the aging parameterization), to emission input data, and to simulated OH levels can be responsible for this behavior. Despite these uncertainties, the implementation of the VBS scheme into the CHIMERE model allowed for much more realistic organic aerosol simulations for Paris during summertime. The advection of SOA from outside Paris is mostly responsible for the highest OA concentration levels. During advection of polluted air masses from northeast (Benelux and Central Europe), simulations indicate high levels of both anthropogenic and biogenic SOA fractions, while biogenic SOA dominates during periods with advection from Southern France and Spain.
High uncertainties affect black carbon (BC) emissions, and, despite its important impact on air pollution and climate, very few BC emissions evaluations are found in the literature. This paper ...presents a novel approach, based on airborne measurements across the Paris, France, plume, developed in order to evaluate BC and NOx emissions at the scale of a whole agglomeration. The methodology consists in integrating, for each transect, across the plume observed and simulated concentrations above background. This allows for several error sources (e.g., representativeness, chemistry, plume lateral dispersion) to be minimized in the model used. The procedure is applied with the CHIMERE chemistry-transport model to three inventories - the EMEP inventory and the so-called TNO and TNO-MP inventories - over the month of July 2009. Various systematic uncertainty sources both in the model (e.g., boundary layer height, vertical mixing, deposition) and in observations (e.g., BC nature) are discussed and quantified, notably through sensitivity tests. Large uncertainty values are determined in our results, which limits the usefulness of the method to rather strongly erroneous emission inventories. A statistically significant (but moderate) overestimation is obtained for the TNO BC emissions and the EMEP and TNO-MP NOx emissions, as well as for the BC / NOx emission ratio in TNO-MP. The benefit of the airborne approach is discussed through a comparison with the BC / NOx ratio at a ground site in Paris, which additionally suggests a spatially heterogeneous error in BC emissions over the agglomeration.
The air pollution abatement consequences for limestone and window glass during the recent period (1997–2014) were quantified in Paris by a 3-step approach: (1) in-the-field measurement of pollution ...and climatic parameters; (2) weathering calculation by means of dose–response functions in 100 m × 100 m grid cells of the Paris plan; (3) mapping the geographic distribution of the calculated damage. In order to get a global damage estimation of different materials, a set of maps were generated: (1) the total surface of buildings and monuments façades in the part of Paris inscribed on the UNESCO List between the Ile Saint-Louis and the Concorde Square; (2) the surface of limestone and window glass of each façade; (3) the yearly spatial distribution of SO
2
, NO
2
and PM10 concentration; (4) the potential surface damage of materials in response to climatic and pollution doses. The calculated responses are in agreement with those measured in the field during several campaigns of exposure of limestone and window glass in Paris performed during the same period; (5) the effective damage to limestone and window glass. The decreases of the potential and of the effective damage are quantified and mapped. They are driven by the decrease in air pollutant concentrations.
Besides their impacts on health, BTEX play an important role in the formation of secondary organic aerosols and ozone for which limit values are regularly exceeded in Paris megacity and Ile de France ...region. An enrichment by a factor of 3 in the C7-C9 aromatic fraction in the Paris atmosphere compared to other northern mid-latitude cities was shown in 2013. Here, we combined different approaches to investigate the role of transport-related sources in such enrichment (gasoline composition and vehicle fleet composition): a statistical analysis of a large BTEX dataset including multi-year and multi-site measurements (traffic, background, tunnel) and a coupled experimental and modelling analysis of liquid and headspace composition of representative fuels distributed in Ile de France region (SP95, SP95 E10, and SP98). For the latter the experimental setup was designed to analyze the composition of 87 VOCs from C2 to C17 in both liquid and headspace phases. The model is able to predict the headspace composition at AE 15% and with an R 2 > 0.9. First a strong positive spatial gradient in BTEX composition at traffic stations is observed, with higher TEX-to-benzene ratio in Paris center compared to the suburbs and outskirts up to a factor of 2. This gradient reflects differences in fleet composition especially gasoline powered vehicles in Paris with a larger proportion of two-wheelers (15% in 2012). This gradient is also consistent with the inter-annual increase of TEX-to-benzene ratios along with the doubling of two-wheelers use and the decrease in the number of passenger cars. The gasoline evaporation model cannot solely explain the observed spatial variability. Finally, we investigated the potential contribution of two-wheelers to the aromatic enrichment in IdF region by introducing an additional unburned gasoline term to the model. The results support the suggestion that two-wheelers are a potential contributor to this enrichment. Considering the high use of two-wheelers in other European cities such as London or Barcelona if Europe is to decrease transport-related air pollution and inner city traffic, policy makers should consider finding alternatives to the conventionally-powered two-wheelers and supporting electric two-wheelers for example.
Measurements of the mole fraction of the CO2 and its isotopes were performed in Paris during the MEGAPOLI winter campaign (January-February 2010). Radiocarbon (14 CO2 ) measurements were used to ...identify the relative contributions of 77% CO2 from fossil fuel consumption (CO2 ff from liquid and gas combustion) and 23% from biospheric CO2 (CO2 from the use of biofuels and from human and plant respiration: CO2 bio). These percentages correspond to average mole fractions of 26.4 ppm and 8.2 ppm for CO2 ff and CO2 bio, respectively. The 13 CO2 analysis indicated that gas and liquid fuel contributed 70% and 30%, respectively, of the CO2 emission from fossil fuel use. Continuous measurements of CO and NOx and the ratios CO/CO2 ff and NOx /CO2 ff derived from radiocarbon measurements during four days make it possible to estimate the fossil fuel CO2 contribution over the entire campaign. The ratios CO/CO2 ff and NOx /CO2 ff are functions of air mass origin and exhibited daily ranges of 7.9 to 14.5 ppb ppm-1 and 1.1 to 4.3 ppb ppm-1 , respectively. These ratios are consistent with different emission inventories given the uncertainties of the different approaches. By using both tracers to derive the fossil fuel CO2 , we observed similar diurnal cycles with two maxima during rush hour traffic.
Atmospheric concentration measurements are used to adjust the daily to monthly budget of fossil fuel CO2 emissions of the Paris urban area from the prior estimates established by the Airparif local ...air quality agency. Five atmospheric monitoring sites are available, including one at the top of the Eiffel Tower. The atmospheric inversion is based on a Bayesian approach, and relies on an atmospheric transport model with a spatial resolution of 2 km with boundary conditions from a global coarse grid transport model. The inversion adjusts prior knowledge about the anthropogenic and biogenic CO2 fluxes from the Airparif inventory and an ecosystem model, respectively, with corrections at a temporal resolution of 6 h, while keeping the spatial distribution from the emission inventory. These corrections are based on assumptions regarding the temporal autocorrelation of prior emissions uncertainties within the daily cycle, and from day to day. The comparison of the measurements against the atmospheric transport simulation driven by the a priori CO2 surface fluxes shows significant differences upwind of the Paris urban area, which suggests a large and uncertain contribution from distant sources and sinks to the CO2 concentration variability. This contribution advocates that the inversion should aim at minimising model–data misfits in upwind–downwind gradients rather than misfits in mole fractions at individual sites. Another conclusion of the direct model–measurement comparison is that the CO2 variability at the top of the Eiffel Tower is large and poorly represented by the model for most wind speeds and directions. The model's inability to reproduce the CO2 variability at the heart of the city makes such measurements ill-suited for the inversion. This and the need to constrain the budgets for the whole city suggests the assimilation of upwind–downwind mole fraction gradients between sites at the edge of the urban area only. The inversion significantly improves the agreement between measured and modelled concentration gradients. Realistic emissions are retrieved for two 30-day periods and suggest a significant overestimate by the AirParif inventory. Similar inversions over longer periods are necessary for a proper evaluation of the optimised CO2 emissions against independent data.
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