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

Raut, Jean-Christophe; Chazette, Patrick

doi:10.5194/acp-8-901-2008

Cited by 53 publications

(37 citation statements)

References 48 publications

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“…For global model, in Chin et al (2002), AOT is overestimated at low aerosol levels, but simulated AOT agree within a factor of 2 and an overall correlation of 70% for monthly data and for all considered stations. AOT computed in Ginoux et al (2006) 0.90, which is coherent with the values obtained for the ES-QUIF experiment (Raut and Chazette, 2007b;Chazette et al, 2005). In the southeastern part of France, simulated SSA ranges here from 0.91 to 0.93, that is in the range 0.85±0.5 found in Mallet et al (2003).…”

Section: Statistic Indicator Definitionsupporting

confidence: 86%

Simulation of aerosol optical properties over Europe with a 3-D size-resolved aerosol model: comparisons with AERONET data

et al. 2008

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Abstract. This paper aims at presenting a model-to-data comparison of the Aerosol Optical Thickness (AOT) and of a few sparse data for Single Scattering Albedo (SSA) over Europe for one year. The main contribution of this paper is the sensitivity study to a large number of parameters, including physical and numerical parameters of the aerosol model itself. The optical parameters are computed from a sizeresolved aerosol model embedded in the POLYPHEMUS system. The methodology is first described, showing that several hypothesis can be made for micro-physical aerosol properties. The simulation is made over one year (2001); statistics and monthly time series for the simulation and AERONET data are used to evaluate the ability of the model to reproduce AOT and vertically averaged SSA fields and their variability. The relation with the uncertainties of measurements is discussed. Then a sensitivity study with respect to the mixing state of the particle, the way to take into account water uptake, numerical parameters and physical parameterizations of the model is carried out. The results indicate that the mixing state of particles has an influence on optical parameters, as well as the computation of the wet diameter. But some physical and numerical parameters associated with the aerosol model itself have even more influence under certain conditions, through the uncertainties on the aerosol chemical composition, and their size distribution.

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Section: Statistic Indicator Definitionsupporting

confidence: 86%

Simulation of aerosol optical properties over Europe with a 3-D size-resolved aerosol model: comparisons with AERONET data

et al. 2008

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“…Uncertainties on the measured (horizontal bars) scattering and absorption coefficients are also shown in the plots. Raut and Chazette, 2008). Larger values of both n and k are instead obtained here compared to AERONET retrievals at different sites in the Western Mediterranean (1.38-1.46 for n and 0.003-0.01 for k at 440 and 670 nm; Mallet et al, 2013).…”

Section: Complex Refractive Index Of Pollution Aerosolsmentioning

confidence: 59%

“…With the aim of understanding which of the two instruments measures correctly in the 0.4-1.0 µm range we performed an optical test, which consisted in calculating with Mie theory the scattering coefficient at 450, 550, and 700 nm based on the PCASP and GRIMM size data, and then in comparing it with simultaneous nephelometer measurements. Optical calculations were performed by fixing the complex refractive index at 1.6 − 0.01 i, so at the mean of the range of values reported in the literature for pollution aerosols (Ebert et al, 2002(Ebert et al, , 2004Mallet et al, 2003Mallet et al, , 2011Müller et al, 2002;Raut and Chazette, 2008). SLRs characterized by a low variability in terms of scattering coefficient and particle concentration were selected.…”

Section: Aircraft Observationsmentioning

confidence: 99%

Continental pollution in the Western Mediterranean basin: large variability of the aerosol single scattering albedo and influence on the direct shortwave radiative effect

et al. 2016

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Abstract. Pollution aerosols strongly influence the composition of the Western Mediterranean basin, but at present little is known on their optical properties. We report in this study in situ observations of the single scattering albedo (ω) of pollution aerosol plumes measured over the Western Mediterranean basin during the TRAQA (TRansport and Air QuAlity) airborne campaign in summer 2012. Cases of pollution export from different source regions around the basin and at different altitudes between ∼ 160 and 3500 m above sea level were sampled during the flights. Data from this study show a large variability of ω, with values between 0.84-0.98 at 370 nm and 0.70-0.99 at 950 nm. The single scattering albedo generally decreases with the wavelength, with some exception associated to the mixing of pollution with sea spray or dust particles over the sea surface. The lowest values of ω (0.84-0.70 between 370 and 950 nm) are measured in correspondence of a fresh plume possibly linked to ship emissions over the basin. The range of variability of ω observed in this study seems to be independent of the source region around the basin, as well as of the altitude and aging time of the plumes. The observed variability of ω reflects in a large variability for the complex refractive index of pollution aerosols, which is estimated to span in the large range 1.41-1.77 and 0.002-0.097 for the real and the imaginary parts, respectively, between 370 and 950 nm.Radiative calculations in clear-sky conditions were performed with the GAME radiative transfer model to test the sensitivity of the aerosol shortwave Direct Radiative Effect (DRE) to the variability of ω as observed in this study. Results from the calculations suggest up to a 50 and 30 % change of the forcing efficiency (FE), i.e. the DRE per unit of optical depth, at the surface (−160/−235 W m −2 τ −1 at 60 • solar zenith angle) and at the Top-Of-Atmosphere (−137/−92 W m −2 τ −1 ) for ω varying between its maximum and minimum value. This induces a change of up to an order of magnitude (+23/+143 W m −2 τ −1 ) for the radiative effect within the atmosphere.

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“…The uncertainty due to LR at 532 nm has been discussed in several papers (e.g. Raut and Chazette, 2008a). This is a major source of uncertainty depending on the constraint used.…”

Section: Uncertainties On Lrmentioning

confidence: 99%

Synergy between CALIOP and MODIS instruments for aerosol monitoring: application to the Po Valley

et al. 2010

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Abstract. In this study aerosol optical properties are studied over the Po Valley from June 2006 to February 2009 using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations/Cloud-Aerosol LIdar with Orthogonal Polarization (CALIPSO/CALIOP) and Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua and Terra. The choice of the Po valley has been driven by the numerous occurrences of pollutant events leading to a mean MODIS-derived aerosol optical depth (AOD) of 0.27 (±0.17) at 550 nm over a large area of ∼120 000 km 2 . AOD derived from MODIS, AERONET and CALIOP have been compared. The comparison with AERONET sunphotometers has highlighted an overestimation of AOD from MODIS radiometers of 0.047 for Aqua and 0.088 for Terra. A systematic underestimation of AOD derived from CALIOP Level-2 products has been observed in comparison to Aqua (0.060) and Terra (0.075) MODIS values. Considering those discrepancies a synergistic approach combining CALIOP level-1 data and MODIS AOD has been developed for the first time over land to retrieve the equivalent extinction-tobackscatter ratio at 532 nm (LR). MODIS-derived AOD were indeed used to constrain CALIOP profiles inversion. A significant number of CALIOP level-1 vertical profiles have been averaged (∼200 individual laser shots) in the Po Valley, leading to a signal-to-noise ratio (SNR) higher than 10 in the planetary boundary layer (PBL), which is suffiCorrespondence to: P. Royer (philippe.royer@lsce.ipsl.fr) cient to invert the mean lidar profiles. The mean LR (together with the associated variabilities) over the Po Valley retrieved from the coupling between CALIOP/MODIS-Aqua and CALIOP/MODIS-Terra are ∼78±22 sr and ∼86±27 sr, respectively. The total uncertainty on LR retrieval has been assessed to be ∼12 sr using a Monte Carlo approach. The mean LR determined from a look-up table through a selection algorithm in CALIOP level 2 operational products (∼63±8 sr) show a good agreement for daytime inversion (70±11 sr for Aqua and 74±14 sr for Terra). These values appear close to what is expected for pollution aerosols in an urban area. Contrarily large differences are observed when considering nighttime CALIOP profiles inverted with daytime AOD from MODIS (63±7 sr for CALIOP level-2 compared with 89±28 sr for CALIOP/Aqua and 103±32 sr for CALIOP/Terra synergies). They can be explained by a significant evolution of AOD between lidar and radiometer passing times. In most of cases, the mean aerosol extinction coefficient in the PBL significantly differs between the level-2 operational products and the result CALIPSO/MODIS synergy results. Mean differences of 0.10 km −1 (∼50%) and 0.13 km −1 (∼60%) have indeed been calculated using MODIS-Aqua/CALIOP and MODIS-Terra/CALIOP coupling studies, respectively. Such differences may be due to the identification of the aerosol model by the operational algorithm and thus to the choice of the LR.Published by Copernicus Publications on behalf of the European Geosciences Union.

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

Cited by 53 publications

References 48 publications

Simulation of aerosol optical properties over Europe with a 3-D size-resolved aerosol model: comparisons with AERONET data

Simulation of aerosol optical properties over Europe with a 3-D size-resolved aerosol model: comparisons with AERONET data

Continental pollution in the Western Mediterranean basin: large variability of the aerosol single scattering albedo and influence on the direct shortwave radiative effect

Synergy between CALIOP and MODIS instruments for aerosol monitoring: application to the Po Valley

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