For the investigation of megacity emission plume characteristics mobile aerosol and trace gas measurements were carried out in the greater Paris region in July 2009 and January–February 2010 within ...the EU FP7 MEGAPOLI project (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation). The deployed instruments measured physical and chemical properties of sub-micron aerosol particles, gas phase constituents of relevance for urban air pollution studies and meteorological parameters. The emission plume was identified based on fresh pollutant (e.g., particle-bound polycyclic aromatic hydrocarbons, black carbon, CO2 and NOx) concentration changes in combination with wind direction data. The classification into megacity influenced and background air masses allowed a characterization of the emission plume during summer and winter environmental conditions. On average, a clear increase of fresh pollutant concentrations in plume compared to background air masses was found for both seasons. For example, an average increase of 190% (+ 8.8 ng m−3) in summer and of 130% (+ 18.1 ng m−3) in winter was found for particle-bound polycyclic aromatic hydrocarbons in plume air masses. The aerosol particle size distribution in plume air masses was influenced by nucleation and growth due to coagulation and condensation in summer, while in winter only the latter process (i.e., particle growth) seemed to be initiated by urban pollution. The observed distribution of fresh pollutants in the emission plume – its cross sectional Gaussian-like profile and the exponential decrease of pollutant concentrations with increasing distance to the megacity – are in agreement with model results. Differences between model and measurements were found for plume center location, plume width and axial plume extent. In general, dilution was identified as the dominant process determining the axial variations within the Paris emission plume. For in-depth analysis of transformation processes occurring in the advected plume, simultaneous measurements at a suburban measurement site and a stationary site outside the metropolitan area using the mobile laboratory have proven to be most useful. Organic aerosol oxidation was observed in summer, while in winter transformation processes seemed to occur at a slower rate.
Aerosol modeling is a challenging scientific problem aimed at improving our knowledge in the many complex processes involved in multiphase chemistry and transport. Correct simulations of aerosols are ...also required in order to elaborate particle emission reduction strategies. The CHIMERE chemistry transport model (Atmos. Environ. 35 (2001) 6277) has been improved to account for particle transport, formation, deposition at the European scale. The aerosol model accounts both for inorganic
(NO
3
−
,
SO
4
2−
,
NH
4
+)
and organic species of primary or secondary origin. Secondary organic aerosols from biogenic and anthropogenic gas precursors are partitioned into gas and particulate phases through a temperature dependent partition coefficient. The modeling approach is presented in this paper with preliminary simulation results over Europe. Comparisons with available data at background stations give acceptable results on PM
10, with correlation coefficients usually exceeding 0.5 and normalized errors in the 30–80% range in many regions. However, results on sulfate, nitrate and ammonium species display less correct error statistics. Comparisons on sulfate concentrations give normalized errors in the range 30–80% in summer and less correct in winter. Temporal correlation coefficients usually range from 0.30 to 0.70. Nitrate concentrations are better simulated during winter than during summer. Difficulties in simulating heterogeneous and aqueous phase processes could explain model deficiencies. Moreover, temperature dependence of gas/particle partitioning processes for nitrate, ammonium and secondary organic species could mainly explain the seasonal variability of biases. Model deficiencies are observed in Southern countries, certainly due to natural dust emissions and resuspended particles. Finally, sea salts seems to have a quite significant influence on error statistics in coastal areas.
We compare tropospheric column densities (vertically integrated concentrations) of NO2 from three data sets for the metropolitan area of Paris during two extensive measurement campaigns (25 days in ...summer 2009 and 29 days in winter 2010) within the European research project MEGAPOLI. The selected data sets comprise a regional chemical transport model (CHIMERE) as well as two observational data sets: ground-based mobile Multi-AXis-Differential Optical Absorption Spectroscopy (car-MAX-DOAS) measurements and satellite measurements from the Ozone Monitoring Instrument (OMI). On most days, car-MAX-DOAS measurements were carried out along large circles (diameter ∼ 35 km) around Paris. The car-MAX-DOAS results are compared to coincident data from CHIMERE and OMI. All three data sets have their specific strengths and weaknesses, especially with respect to their spatiotemporal resolution and coverage as well as their uncertainties. Thus we compare them in two different ways: first, we simply consider the original data sets. Second, we compare modified versions making synergistic use of the complementary information from different data sets. For example, profile information from the regional model is used to improve the satellite data, observations of the horizontal trace gas distribution are used to adjust the respective spatial patterns of the model simulations, or the model is used as a transfer tool to bridge the spatial scales between car-MAX-DOAS and satellite observations. Using the modified versions of the data sets, the comparison results substantially improve compared to the original versions. In general, good agreement between the data sets is found outside the emission plume, but inside the emission plumes the tropospheric NO2 vertical column densities (VCDs). are systematically underestimated by the CHIMERE model and the satellite observations (compared to the car-MAX-DOAS observations). One major result from our study is that for satellite validation close to strong emission sources (like power plants or megacities), detailed information about the intra-pixel heterogeneity is essential. Such information may be gained from simultaneous car-MAX-DOAS measurements using multiple instruments or by combining (car-) MAX-DOAS measurements with results from regional model simulations.
Partial lower tropospheric ozone columns provided by the IASI (Infrared Atmospheric Sounding Interferometer) instrument have been assimilated into a chemistry-transport model at continental scale ...(CHIMERE) using an Ensemble Square Root Kalman Filter (EnSRF). Analyses are made for the month of July 2007 over the European domain. Launched in 2006, aboard the MetOp-A satellite, IASI shows high sensitivity for ozone in the free troposphere and low sensitivity at the ground; therefore it is important to evaluate if assimilation of these observations can improve free tropospheric ozone, and possibly surface ozone. The analyses are validated against independent ozone observations from sondes, MOZAIC1 aircraft and ground based stations (AIRBASE – the European Air quality dataBase) and compared with respect to the free run of CHIMERE. These comparisons show a decrease in error of 6 parts-per-billion (ppb) in the free troposphere over the Frankfurt area, and also a reduction of the root mean square error (respectively bias) at the surface of 19% (33%) for more than 90% of existing ground stations. This provides evidence of the potential of data assimilation of tropospheric IASI columns to better describe the tropospheric ozone distribution, including surface ozone, despite the lower sensitivity. The changes in concentration resulting from the observational constraints were quantified and several geophysical explanations for the findings of this study were drawn. The corrections were most pronounced over Italy and the Mediterranean region, we noted an average reduction of 8–9 ppb in the free troposphere with respect to the free run, and still a reduction of 5.5 ppb at ground, likely due to a longer residence time of air masses in this part associated to the general circulation pattern (i.e. dominant western circulation) and to persistent anticyclonic conditions over the Mediterranean basin. This is an important geophysical result, since the ozone burden is large over this area, with impact on the radiative balance and air quality. 1 Measurements of OZone, water vapour, carbon monoxide and nitrogen oxides by in-service AIrbus airCraft (http://mozaic.aero.obs-mip.fr/web/).
We describe a computational technology for studying the effects of the aerosol-radiation interaction and calculating regional estimates of the direct (DRE) and semidirect radiative effects (SDRE) of ...biomass burning (BB) aerosol based on simulations with the CHIMERE chemistry transport model coupled with the WRF meteorological model. The technology was applied to numerical studying the radiative effects of Siberian biomass burning aerosol in the eastern Arctic in the period of July 16–31, 2016. The model simulations show that Siberian smokes, on the whole, had a significant cooling effect on the atmosphere in the eastern Arctic in that period due to the DRE, the value of which at top of the atmosphere was, on average, −6.0 W m
−2
, being minimal over the snow-ice cover of the ocean (−1.2 W m
−2
). At the same time, the contribution of the Siberian BB aerosol DRE to the radiative balance of the Arctic atmosphere is found to be offset to a certain extent by the SDRE, which is positive (2.0 W m
−2
), on average. The SDRE is formed as a result of the multihour aerosol effect on meteorological processes and plays the most important role over the snow-ice Arctic covers, where it exceeds the DRE in absolute value. It has been shown that the SDRE of Siberian BBA in our numerical experiments is mainly due to scattering (rather than absorption) of radiation by aerosol particles.
Multiannual satellite measurements of tropo-spheric NO 2 columns are used for evaluation of CO 2 emission changes in China in the period from 1996 to 2008. Indirect top-down annual estimates of CO 2 ...emissions are derived from the satellite NO 2 column measurements by means of a simple inverse modeling procedure involving simulations performed with the CHIMERE mesoscale chemistry-transport model and the CO 2-to-NO x emission ratios from the Emission Database for Global Atmospheric Research (EDGAR) global anthropogenic emission inventory and Regional Emission Inventory in Asia (REAS). Exponential trends in the normalized time series of annual emissions are evaluated separately for the periods from 1996 to 2001 and from 2001 to 2008. The results indicate that the both periods manifest strong positive trends in the CO 2 emissions , and that the trend in the second period was significantly larger than the trend in the first period. Specifically, the trends in the first and second periods are best estimated to be in the range from 3.7 to 8.3 and from 11.0 to 13.2 % per year, respectively, taking into account statistical uncertainties and differences between the CO 2-to-NO x emission ratios from the EDGAR and REAS inventories. Comparison of our indirect top-down estimates of the CO 2 emission changes with the corresponding bottom-up estimates provided by the EDGAR (version 4.2) and Global Carbon Project (GCP) glomal emission inventories reveals that while acceleration of the CO 2 emission growth in the considered period is a common feature of both kinds of estimates, non-linearity in the CO 2 emission changes may be strongly exaggerated in the global emission inventories. Specifically, the atmospheric NO 2 observations do not confirm the existence of a sharp bend in the emission inventory data time series in the period from 2000 to 2002. A significant quantitative difference is revealed between the bottom-up and indirect top-down estimates of the CO 2 emission trend in the period from 1996 to 2001 (specifically, the trend was not positive according to the global emission inventories, but is strongly positive in our estimates). These results confirm the findings of earlier studies that indicated probable large uncertainties in the energy production and other activity data for China from international energy statistics used as the input information in the global emission inventories. For the period from 2001 to 2008, some quantitative differences between the different kinds of estimates are found to be in Published by Copernicus Publications on behalf of the European Geosciences Union. 9416 E. V. Berezin et al.: Multiannual changes of CO 2 emissions in China the range of possible systematic uncertainties associated with our estimation method. In general, satellite measurements of tropospheric NO 2 are shown to be a useful source of information on CO 2 sources collocated with sources of nitrogen oxides; the corresponding potential of these measurements should be exploited further in future studies.
The approach of Bayesian Monte Carlo analysis has been used for evaluating model uncertainty in ozone production and its sensitivity to emission changes. This approach has been applied to the ozone ...fields calculated by the CHIMERE regional model in the Ile‐de‐France area during the 1998 and 1999 summer seasons. The AIRPARIF network measurements of urban NO and O3 concentrations and rural O3 over the Ile‐de‐France region have been used for constraining the Monte Carlo simulations. Our results yield the following major conclusions: (1) The simulated formation of O3 plumes are mainly located in southwestern to southeastern directions downwind the Paris area. (2) Uncertainties on simulated ozone concentrations and several derived quantities are evaluated and reduced using the BMC approach; simulated urban and plume ozone concentrations are enhanced through the observational constraint as compared to those obtained from the unconstrained model. (3) The chemical regime over the urban area of Paris and within plumes is clearly VOC sensitive on the average over two summers. This statement is robust with respect to the BMC uncertainty analysis.
The recent important developments in satellite measurements of the composition of the lower atmosphere open the challenging perspective to use such measurements as independent information on sources ...and sinks of atmospheric pollutants. This study explores the possibility to improve estimates of gridded NOx emissions used in a continental scale chemistry transport model (CTM), CHIMERE, by employing measurements performed by the GOME and SCIAMACHY instruments. We set-up an original inverse modelling scheme that not only enables a computationally efficient optimisation of the spatial distribution of seasonally averaged NOx emissions (during summertime), but also allows estimating uncertainties in input data and a priori emissions. The key features of our method are (i) replacement of the CTM by a set of empirical models describing the relationships between tropospheric NO2 columns and NOx emissions with sufficient accuracy, (ii) combination of satellite data for tropospheric NO2 columns with ground based measurements of near surface NO2 concentrations, and (iii) evaluation of uncertainties in a posteriori emissions by means of a special Bayesian Monte-Carlo experiment which is based on random sampling of errors of both NO2 columns and emission rates. We have estimated the uncertainty in a priori emissions based on the EMEP emission inventory to be about 1.9 (in terms of geometric standard deviation) and found the uncertainty in a posteriori emissions obtained from our inverse modelling scheme to be significantly lower (about 1.4). It is found also that a priori NOx emission estimates are probable to be persistently biased in many regions of Western Europe, and that the use of a posteriori emissions in the CTM improves the agreement between the modelled and measured data.
Formaldehyde (HCHO) is an important intermediate compound in the degradation of volatile organic compounds (VOCs) in the troposphere. Sources of HCHO are largely dominated by its secondary production ...from VOC oxidation, methane and isoprene being the main precursors in unpolluted areas. As a result of the moderate lifetime of HCHO, its spatial distribution is determined by reactive hydrocarbon emissions. We focus here on Europe and investigate the influence of the different emissions on HCHO tropospheric columns with the CHIMERE chemical transport model in order to interpret the comparisons between SCIAMACHY and simulated HCHO columns. Europe was never specifically studied before for these purposes using satellite observations. The bias between measurements and model is less than 20% on average. The differences are discussed according to the errors on the model and the observations and remaining discrepancies are attributed to a misrepresentation of biogenic emissions. This study requires the characterisation of: (1) the model errors and performances concerning formaldehyde. The errors on the HCHO columns, mainly related to chemistry and mixed emission types, are evaluated to 2×1015 molecule/cm2 and the model performances evaluated using surface measurements are satisfactory (~13%); (2) the observation errors that define the needs in spatial and temporal averaging for meaningful comparisons. Using SCIAMACHY observations as constraint for biogenic isoprene emissions in an inverse modelling scheme reduces their uncertainties by about a factor of two in region of intense emissions. The retrieved correction factors for the isoprene emissions range from a factor of 0.15 (North Africa) to a factor of 2 (Poland, the United Kingdom) depending on the regions.
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.
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