Laboratory investigation of the optical absorption properties of brown carbon in the CESAM simulation chamber using a photoacoustic spectrophone at 405 nm

Light absorption by atmospheric aerosol particles, such as black and brown carbon (BC and BrC), has important effects on the Earth’s radiative balance and climate. Accurate knowledge of the optical absorption properties of such carbonaceous aerosols is highly needed in order to provide the necessary parameterizations for climate models and for remote sensing in order to constrain their global and regional radiative effect. Nowadays, large-scale model calculations are still too poorly constrained to make sufficiently accurate assessments of the climate effects of absorbing aerosols [1]. In this context, filter-free measurement technique based on photoacoustic spectrophone (PAS) has been developed in order to provide in situ measurements of light absorption by aerosols in their natural suspended state to avoid the measurement artefacts associated with traditional, filter-based absorption photometers. In the framework of the ANR B2C project, a custom-made PAS operating at 405 nm has been deployed for filter-free measurement of absorption coefficient of brown carbon, produced from oxidation of naphthalene by OH radicals in the CESAM atmospheric simulation chamber [2,3]. Performances of the deployed PAS has been evaluated and characterized with the help of the reference instruments deployed in the measurement campaign, such as aethalometer (AE33), scanning mobility particle sizer (SMPS), NOx Monitor (APNA-370) and TEOM monitor (based on tapered element oscillating microbalances technology). Experimental details and the preliminary results will be discussed and presented. Acknowledgments This work is partially supported by the French national research agency (ANR) under the B2C (ANR-19-CE01-0024), Labex CaPPA (ANR-10-LABX-005) and PIA-ADEME SEAM contracts, the CPER ECRIN program, and the EU H2020-ATMOS project. The CNRS-INSU is gratefully acknowledged for supporting the CESAM chamber as a national facility as well as the AERIS data center for distributing and curing the data produced by the CESAM chamber. References [1] C. Cappa, R. Kotamarthi, A. Sedlacek, C. Flynn, E. Lewis, A. McComiskey, N. Riemer, "Absorbing Aerosols Workshop Report", U.S. Department of Energy, Climate and Environmental Sciences Division, January 20-21, 2016. [2] J. Wang, J. F. Doussin, S. Perrier, E. Perraudin, Y. Katrib, E. Pangui, and B. Picquet-Varrault, "Design of a new multi-phase experimental simulation chamber for atmospheric photosmog, aerosol and cloud chemistry research", Atmos. Meas. Tech. 4 (2011) 2465–2494 [3] H. Yi, M. Cazaunau, A. Gratien, V. Michoud, E. Pangui, J.-F. Doussin, W. Chen, "Intercomparison of IBBCEAS, NitroMAC and FTIR for HONO, NO2 and CH2O measurements during the reaction of NO2 with H2O vapour in the simulation chamber CESAM", Atmos. Meas. Tech. 14 (2021) 5701–5715