Aerosol chemical and optical properties over the Paris area within ESQUIF project

Abstract

Abstract. Aerosol chemical and optical properties are extensively investigated for the first time over the Paris Basin in July 2000 within the ESQUIF project. The measurement campaign offers an exceptional framework to evaluate the performances of the chemistry-transport model CHIMERE in simulating concentrations of gaseous and aerosol pollutants, as well as the aerosol-size distribution and composition in polluted urban environments against ground-based and airborne measurements. A detailed comparison of measured and simulated variables during the second half of July with particular focus on 19 and 31 pollution episodes reveals an overall good agreement for gas-species and aerosol components both at the ground level and along flight trajectories, and the absence of systematic biases in simulated meteorological variables such as wind speed, relative humidity and boundary layer height as computed by the MM5 model. A good consistency in ozone and NO concentrations demonstrates the ability of the model to reproduce the plume structure and location fairly well both on 19 and 31 July, despite an underestimation of the amplitude of ozone concentrations on 31 July. The spatial and vertical aerosol distributions are also examined by comparing simulated and observed lidar vertical profiles along flight trajectories on 31 July and confirm the model capacity to simulate the plume characteristics. The comparison of observed and modeled aerosol components in the southwest suburb of Paris during the second half of July indicates that the aerosol composition is rather correctly reproduced, although the total aerosol mass is underestimated by about 20%. The simulated Parisian aerosol is dominated by primary particulate matter that accounts for anthropogenic and biogenic primary particles (40%), and inorganic aerosol fraction (40%) including nitrate (8%), sulfate (22%) and ammonium (10%). The secondary organic aerosols (SOA) represent 12% of the total aerosol mass, Correspondence to: A. Hodzic (hodzic@lmd.polytechnique.fr) while the mineral dust accounts for 8%. The comparison demonstrates the absence of systematic errors in the simulated sulfate, ammonium and nitrates total concentrations. However, for nitrates the observed partition between fine and coarse mode is not reproduced. In CHIMERE there is a clear lack of coarse-mode nitrates. This calls for additional parameterizations in order to account for the heterogeneous formation of nitrate onto dust particles. Larger discrepancies are obtained for the secondary organic aerosols due to both inconsistencies in the SOA formation processes in the model leading to an underestimation of their mass and large uncertainties in the determination of the measured aerosol organic fraction. The observed mass distribution of aerosols is not well reproduced, although no clear explanation can be given.

Comparison between simulated and observed chemical composition of fine aerosols in Paris (France) during springtime: contribution of regional versus continental emissions

“…Time-limited information in the chemical composition of fine aerosols in Paris have been recently reported by Gros et al (2007) but for a site impacted by traffic which may not be fully representative for the composition and levels of aerosols in the Paris urban background atmosphere. Modelling studies over Paris have been reported in literature but concerned mainly PM with A.D. <10 µm (PM 10 ) or total suspended matter size fractions (Bessagnet et al, 2005;Hodzic et al, 2006). As a result, chemical composition of PM 2.5 over the region of Paris remains poorly documented and regional model simulating PM 2.5 concentrations and composition over this region poorly constrained.…”

“…The model has been also extensively used to simulate gas phase pollution levels over the Paris region (e.g., Vautard et al, 2001;Beekmann et al, 2003;Derognat et al, 2003;Deguillaume et al, 2007 and, and on several occasions particulate matter (e.g. Bessagnet, 2005;Hodzic et al, 2006).…”

Evaluating simulated primary anthropogenic and biomass burning organic aerosols during MILAGRO: implications for assessing treatments of secondary organic aerosols

“…Measurements during MILAGRO (e.g. Kleinman et al, 2008;de Gouw et al, 2009) and other field campaigns worldwide (de Gouw et al, 2005;Simpson et al, 2007;Hodzic et al, 2006;Zhang et al, 2007) have indicated that, as a result of secondary organic aerosol (SOA) formation processes, organic aerosol mass is much higher than one would expect from primary emissions and dispersion. However, the understanding of how anthropogenic and biogenic precursors contribute to SOA formation is far from complete.…”

Aerosol ageing in an urban plume – implication for climate

“…Several urban plume studies have been carried out within comprehensive but short field campaigns in large cities (> 1 million people), e.g. Mexico City (Doran et al, 2007;Hodzic et al, 2009;Tsimpidi et al, 2010), Tampa (Nolte et al, 2008), Paris (Hodzic et al, 2006) and Copenhagen (Wang et al, 2010), while very few, if any, such studies have been carried out in small to midsize cities (< 1 million people). Still, about 60% of the urban population of the world live in small to midsize cities (Population Div.…”