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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 chemistrytransport 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. [ABSTRACT FROM AUTHOR]

Results of the chemistry transport model CHIMERE are compared with the measurements performed during the MEGAPOLI 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 ag- 5 ing of semi-volatile organic species. Organic aerosol is the main focus and is simulated with three different configurations related to the volatility of POA and the scheme of secondary organic aerosol (SOA) formation. 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 10 concentrations are evaluated and four pollution regimes according to the air mass origin are defined. 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 overes- 15 timates 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. All observed high concentration events are reproduced by the model mostly after long range transport, indicating that long range transport of SOA to Paris is well reproduced. Depending on the emission in- 20 ventory 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 25 more realistic organic aerosol simulations for Paris during summer time. The advection of SOA from outside Paris is mostly responsible for the highest OA concentration levels. During advection of polluted air masses from north-east (Benelux and Central Europe), simulations indicate high levels of both anthropogenic and biogenic SOA fractions, while biogenic SOA dominates during days with advection from Southern France and Spain. [ABSTRACT FROM AUTHOR]

An innovative approach using mobile lidar measurements was implemented to test the performances of chemistry-transport models in simulating mass concentrations (PM10) predicted by chemistry-transport models. A ground-based mobile lidar (GBML) was deployed around Paris onboard a van during the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) summer experiment in July 2009. The measurements performed with this Rayleigh-Mie lidar are converted into PM10 profiles using optical-to-mass relationships previously established from in situ measurements performed around Paris for urban and peri-urban aerosols. The method is described here and applied to the 10 measurements days (MD). MD of 1, 15, 16 and 26 July 2009, corresponding to different levels of pollution and atmospheric conditions, are analyzed here in more details. Lidar-derived PM10 are compared with results of simulations from POLYPHEMUS and CHIMERE chemistry-transport models (CTM) and with ground-based observations from the AIRPARIF network. GBML-derived and AIRPARIF in situ measurements have been found to be in good agreement with a mean Root Mean Square Error RMSE (and a Mean Absolute Percentage Error MAPE) of 7.2 µgm-3 (26.0 %) and 8.8 µgm-3 (25.2 %) with relationships assuming peri-urban and urbantype particles, respectively. The comparisons between CTMs and lidar at ~200m height have shown that CTMs tend to underestimate wet PM10 concentrations as revealed by the mean wet PM10 observed during the 10 MD of 22.4, 20.0 and 17.5 µgm-3 for lidar with peri-urban relationship, and POLYPHEMUS and CHIMERE models, respectively. This leads to a RMSE (and a MAPE) of 6.4 µgm-3 (29.6 %) and 6.4 µgm-3 (27.6 %) when considering POLYPHEMUS and CHIMERE CTMs, respectively. Wet integrated PM10 computed (between the ground and 1 km above the ground level) from lidar, POLYPHEMUS and CHIMERE results have been compared and have shown similar results with a RMSE (and MAPE) of 6.3 mgm-2 (30.1 %) and 5.2 mgm-2 (22.3 %) with POLYPHEMUS and CHIMERE when comparing with lidar-derived PM10 with periurban relationship. The values are of the same order of magnitude than other comparisons realized in previous studies. The discrepancies observed between models and measured PM10 can be explained by difficulties to accurately model the background conditions, the positions and strengths of the plume, the vertical turbulent diffusion (as well as the limited vertical model resolutions) and chemical processes as the formation of secondary aerosols. The major advantage of using vertically resolved lidar observations in addition to surface concentrations is to overcome the problem of limited spatial representativity of surface measurements. Even for the case of a wellmixed boundary layer, vertical mixing is not complete, especially in the surface layer and near source regions. Also a bad estimation of the mixing layer height would introduce errors in simulated surface concentrations, which can be detected using lidar measurements. In addition, horizontal spatial representativity is larger for altitude integrated measurements than for surface measurements, because horizontal inhomogeneities occurring near surface sources are dampened. [ABSTRACT FROM AUTHOR]

An original approach using mobile lidar measurements was implemented to validate mass concentrations (PM10) predicted by chemistry-transport models. A ground-based mobile lidar (GBML) was deployed around Paris onboard a van during the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) summer experiment in July 2009. The measurements performed with this Rayleigh-Mie lidar are converted into PM10 profiles using optical-to-mass relationships previously established from in situ measurements performed around Paris for urban and peri-urban aerosols. The method is described here and applied to the 10 measurements days (MD). MD of 1, 15, 16 and 26 July 2009 correspond to contrasted levels of pollution and atmospheric conditions. They are analyzed here in more details. Lidar-derived PM are compared with results of simulations from POLYPHEMUS and CHIMERE chemistry-transport models (CTM) and with ground-based observations from AIRPARIF network. GBML-derived and AIRPARIF in situ measurements have been found to be in good agreement with a mean Root Mean Square Error RMSE (and a Mean Absolute Percentage Error MAPE) of 5.9 µgm-3 (21.0%) with peri-urban and 8.7 µgm-3 (25.4%) with urban relationships, respectively. The comparisons between CTMs and lidar have shown that CTMs tend to underestimate wet PM concentrations as revealed by the mean wet PM observed during the 10 MD of 22.7, 20.0 and 17.5 µgm-3 for lidar with peri-urban relationship, POLYPHEMUS and CHIMERE models, respectively. This leads to a RMSE (and a MAPE) of 7.2 µgm-3 (33.4%) and 7.4 µgm (32.0%) when considering POLYPHEMUS and CHIMERE CTMs, respectively. Wet integrated PM computed (between the ground and 1 km above the ground level) from lidar, POLYPHEMUS and CHIMERE results have been compared and have shown similar results with a RMSE (and MAPE) of 6.7 µgm-2 (30.7%) and 7.1 µgm-2 (28.4%) with POLYPHEMUS and CHIMERE when comparing with lidar-periu-urban parametrization. The values are of the same order of magnitude than other comparisons realized in previous studies. The discrepancies observed between models and measured PM10 can be explained by difficulties to accurately model the background conditions, the positions and strengths of the plume, the vertical diffusion (as well as the limited vertical model resolutions) and the chemical modeling such as the formation of secondary aerosols. [ABSTRACT FROM AUTHOR]

The article discusses the impact of aerosols on the calculation of nitrogen dioxide airmass factors through a sensitivity study. It notes that the study of aerosols uses a radiative transfer model called SCIATRAN, where aerosols vary from the properties of the particles. It adds that measurements' sensitivity increases or decreases depending on the particle mixed with the trace gas. It also cites the key factors for aerosol properties such as aerosol optical depth and single scattering albedo.

The low index interfacial configuration, interface energy and electronic properties of NbC/α-Fe are calculated using the first-principles method based on density functional theory and ab initio molecular dynamics simulation. Additionally, the NbC/α-Fe interface with the low index interfacial configuration is calculated by two-dimensional disregistry method. It is demonstrated that the Fe-C type has an interface energy of -1.553 J/m², the smallest interface energy and the most stable structure, therefore the Fe-C type is the most stable conformation of the NbC(001)/α-Fe(001). Strong orbital resonance phenomenon exists between Fe-3d, Nb-4d and C-2p, producing strong metallic and covalent bonds. The results of disregistry calculation by different interfacial structures of NbC/α-Fe shows that the disregistry of NbC(001)/α-Fe(001) crystalline surface is the smallest at 10.19%, which corresponds to the results of interface energy calculation. It can be shown that the α-Fe(001) is the optimal orientation surface of the NbC(001). Herein, we have revealed the site-oriented and stable bonding mode relationship of NbC/α-Fe interface in steel, which provides important theoretical guidance to explore the mechanism of grain refinement of NbC particles in shipbuilding steels. [ABSTRACT FROM AUTHOR]