Optical properties of urban aerosol from airborne and ground‐based in situ measurements performed during the Etude et Simulation de la Qualité de l'air en Ile de France (ESQUIF) program

Abstract

International audienceUrban aerosol microphysical and optical properties were investigated over the Paris area coupling, for the first time, with dedicated airborne in situ instruments (nephelometer and particle sizers) and active remote sensor (lidar) as well as ground-based in situ instrumentation. The experiment, covering two representative pollution events, was conducted in the framework of the Etude et Simulation de la Qualité de l'air en Ile de France (ESQUIF) program. Pollution plumes were observed under local northerly and southerly synoptic wind conditions on 19 and 31 July 2000, respectively. The 19 July (31 July) event was characterized by north-northwesterly (westerly) advection of polluted (clean) air masses originating from Great Britain (the Atlantic Ocean). The aerosol number size distribution appeared to be composed mainly of two modes in the planetary boundary layer (accumulation and nucleation) and three modes in the surface layer (accumulation, nucleation, and coarse). The characteristics of the size distribution (modal radii and geometric dispersion) were remarkably similar on both days and very coherent with the aerosol optical parameters retrieved from lidar and nephelometer measurements. The city of Paris mainly produces aerosols in the nucleation mode (modal radius of Å`0.03 É m) that have little influence on the aerosol optical properties in the visible spectral range. The latter are largely dominated by the scattering properties of aerosols in the accumulation mode (modal radius of Å`0.12 É m). When the incoming air mass is already polluted (clear), the aerosol in the accumulation mode is shown to be essentially hydrophobic (hydrophilic) in the outgoing air mass

Parisfog

“…Wind speed and direction were identified as two main factors controlling the local aerosol concentration. The N aer was largest under easterly conditions (25% of occurrences), as shown in Table 6, when the Paris area is exposed to continental air masses and the SIRTA observatory is in the Paris plume (Chazette et al 2005). In 25% of easterly conditions, N aer at SIRTA ranged between 15,000 and 22,000 cm −3 , similar to levels observed in the Po Valley in 1989 and 1994 by Noone et al (1992) and Yuskiewicz et al (1998), respectively.…”

Airborne measurements of trace gases and aerosols over the London metropolitan region

“…In Europe, components of the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) project examined emissions from Paris, France in 2009 and 2010. It followed the original experiments conducted within the frame of the Etude et Simulation de la Qualité de l'air en region Ile-deFrance (ESQUIF) program (Chazette et al, 2005;Menut et al, 2000). Results from these recent campaigns have underscored the importance of oxygenated organic and secondary inorganic aerosol species to PM concentrations even in major urban locations (e.g., Aiken et al, 2009).…”

Vertical profiles of urban aerosol complex refractive index in the frame of ESQUIF airborne measurements

“…Bodhaine et al, 1991;. To take into account the non-observed scattering angles, a correction factor has been assessed, from Mie computations, to be close to 1.035 for urban aerosols (Chazette et al, 2005). This assessment was done using the retrieved aerosol mean size number distribution and the mean complex refractive index during July 2000.…”

“…In this study, ACRI retrieval has been performed in the framework of the Etude et Simulation de la QUalité de l'air en Ile-de-France (ESQUIF) experiment that took place over the Paris area in July 2000, involving airborne measurements (Chazette et al, 2005). Next we relate the variations in the retrieved ACRI to the meteorological conditions during the experiment and discuss their evolution in the atmospheric column by looking at their past and the origin of the air masses.…”