# Aerosol complex refractive index retrieval in the Paris urban area and its forested surroundings during the ACROSS field campaign: variability and constraint for direct radiative effect estimation in regional models

Ludovico Di Antonio, Claudia Di Biagio, Matthias Beekmann, Aline Gratien, Paola Formenti, Astrid Bauville, Antonin Bérge, Joel Ferreira de Brito, Mathieu Cazaunau, Servanne Chevaillier, et al.

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Ludovico Di Antonio, Claudia Di Biagio, Matthias Beekmann, Aline Gratien, Paola Formenti, et al.. Aerosol complex refractive index retrieval in the Paris urban area and its forested surroundings during the ACROSS field campaign: variability and constraint for direct radiative effect estimation in regional models. European Geosciences Union General Assembly 2023, Apr 2023, Vienne, Austria. 10.5194/egusphere-egu23-420 . hal-04199565

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Submitted on 7 Sep 2023

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# Aerosol complex refractive index retrieval in the Paris urban area and its forested surroundings during the ACROSS field campaign: variability and constraint for direct radiative effect estimation in regional models

Ludovico Di Antonio<fnref n="1" />, Claudia Di Biagio<fnref n="2" />, Matthias Beekmann<fnref n="2" />, Aline Gratien<fnref n="2" />, Paola Formenti<fnref n="2" />, Astrid Bauville<fnref n="1" />, Antonin Bérge<fnref n="1" />, Joel Ferreira de Brito<fnref n="3" />, Mathieu Cazaunau<fnref n="2" />, Servanne Chevaillier<fnref n="2" />, Barbara D'Anna<fnref n="4" />, David Owen De Haan<fnref n="5" />, Olivier Favez<fnref n="6" />,<fnref n="11" />, Cecile Gaimoz<fnref n="1" />, Olivier Garret<fnref n="12" />, Leila N. Hawkins<fnref n="7" />, Julien Kammer<fnref n="4" />, Brigitte Language<fnref n="1" />,<fnref n="14" />, Franck Maisonneuve<fnref n="1" />, Griša Močnik<fnref n="8" />, Anne Monod<fnref n="4" />, Gael Noyalet<fnref n="2" />, Diana Pereira<fnref n="2" />, Sebastien Perrier<fnref n="10" />, Jean-Eudes Petit<fnref n="9" />, Drew Pronovost<fnref n="7" />, Véronique Riffault<fnref n="3" />, Sydney Riley<fnref n="7" />, Matthieu Riva<fnref n="10" />, Marwa Shahin<fnref n="4" />, Guillaume Siour<fnref n="2" />, Brice Temime-Roussel<fnref n="4" />, Chenjie Yu<fnref n="2" />, Pascal Zapf<fnref n="2" />, Gilles Foret<fnref n="1" />, Jean-François Doussin<fnref n="1" />, Christopher Cantrell<fnref n="1" />,<fnref n="13" />, and Vincent Michoud<fnref n="2" />

The complex refractive index (CRI) is one of the key parameter driving aerosol spectral optical properties and direct radiative effects (DRE). Its value and spectral variation under different conditions, such as anthropogenic- and biogenic-dominated environments and anthropogenic-biogenic mixing situations, remains not fully understood. As a consequence, oversimplified representations of aerosol optical properties are generally used in climate models. Therefore, measurements of aerosol CRI in different environments and their inclusion in models are needed. The field observations from the ACROSS campaign, performed in June-July 2022 in the

<footnote n="1">¹Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France</footnote>

<footnote n="2">²Université Paris Cité and Univ Paris Est Creteil, CNRS, LISA, F-75013 Paris, France</footnote>

<footnote n="3">³Centre for Energy and Environment, IMT Nord Europe, Institut Mine-Télécom, Université de Lille, Lille, 59000, France</footnote>

<footnote n="4">⁴Aix Marseille Univ, CNRS, LCE, Marseille, France</footnote>

<footnote n="5">⁵Department of Chemistry and Biochemistry, University of San Diego, 5998 Alcala Park, San Diego, California 92110, United States</footnote>

<footnote n="6">⁶Institut National De L'environnement Industriel et Des Risques (INERIS), Parc Technologique Alata BP2, 60550 Verneuil-en-Halatte, France</footnote>

<footnote n="7">⁷Department of Chemistry, Harvey Mudd College, 301 Platt Blvd, Claremont, California 91711, United States</footnote>

<footnote n="8">⁸Center for Atmospheric Research, University of Nova Gorica, Nova Gorica SI-5000, Slovenia</footnote>

<footnote n="9">⁹Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, IPSL, Université Paris-Saclay, 91191 Gif-sur-Yvette, France</footnote>

<footnote n="10">¹⁰Univ. Lyon, Université Claude Bernard Lyon1, CNRS, IRCELYON, 69626 Villeurbanne, France</footnote>

<footnote n="11">¹¹Laboratoire Central de Surveillance de la Qualité de l'Air (LCSQA), 60550, Verneuil-en-Halatte, France</footnote>

<footnote n="12">¹²Ville de Paris, Service parisien de santé environnementale, 75013, Paris, France</footnote>

<footnote n="13">¹³University of Colorado, Atmospheric and Oceanic Sciences (ATOC), Boulder, CO 80309</footnote>

<footnote n="14">¹⁴now at Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa</footnote>
Ile de France region, are used in this study to deepen the knowledge of aerosol optical properties, aiming to improve the aerosol representation in the CHIMERE model and provide the best constraint for DRE simulations. Measurements obtained both at the Paris city center and the Rambouilllet rural forest sites during ACROSS are considered, in order to explore the CRI variability from anthropogenic-dominated to biogenic-dominated environments, including anthropogenic-biogenic mixing situations. The CRI retrievals at seven different wavelengths, performed by combining the Mie theory with optical and size distribution measurements, are representative of different atmospheric conditions, aerosol loadings as well as type and chemical compositions. In fact, the June-July 2022 period was characterized by highly diversified weather conditions: 1) two strong heatwaves, promoting SOA build-up and favoring the export of the Paris pollution plume towards the forest site; 2) Saharan dust events transported from the upper atmosphere to the ground; 3) biomass burning episode; 4) periods with reduced anthropogenic influence. The CRI retrievals under these different conditions and their link to particulate chemical composition is investigated. Hence, the CRI dataset presented here constitutes a unique dataset from which models can benefit to validate and constrain simulations and DRE estimations, under both urban and biogenic emissions influence. These data, in conjunction with those from the aircraft observations during ACROSS, are used to initialize and perform sensitivity studies on the aerosol DRE, using the CHIMERE-WRF coupled model, the OPTSIM model for the aerosol optical properties and the Rapid Radiative Transfer Model for GCMs (RRTMG).

**Keywords:** Complex refractive index, direct radiative effect, aerosol mixing, urban, forest