Comparison of different Aethalometer correction schemes and a reference multi-wavelength absorption technique for ambient aerosol data
Jorge Saturno1, Christopher Pöhlker1, Dario Massabò2, Joel Brito3, Samara Carbone4, Yafang Cheng1, Xuguang Chi5, Florian Ditas1, Isabella Hrabě de Angelis1, Daniel Morán-Zuloaga1, Mira L. Pöhlker1, Luciana V. Rizzo6, David Walter1, Qiaoqiao Wang1, Paulo Artaxo7, Paolo Prati2, and Meinrat O. Andreae1,8,91Max Planck Institute for Chemistry, Biogeochemistry and Multiphase Chemistry Departments, P.O. Box 3060, 55020 Mainz, Germany 2Department of Physics & INFN, University of Genoa, via Dodecaneso 33, 16146, Genova, Italy 3Laboratory for Meteorological Physics, University Blaise Pascal, Clermont-Ferrand, France 4Institute of Agrarian Sciences, Federal University of Uberlândia, Uberlândia, Minas Gerais, Brazil 5Institute for Climate and Global Change and School of Atmospheric Sciences, Nanjing University, China 6Department of Earth and Exact Sciences, Institute of Environmental, Chemical and Pharmaceutics Sciences, Federal University of São Paulo, São Paulo, Brazil 7Department of Applied Physics, Institute of Physics, University of São Paulo, Rua do Matão, Travessa R, 187, CEP 05508-900, São Paulo, SP, Brazil 8Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92098, USA 9Geology and Geophysics Department, King Saud University, Riyadh, Saudi Arabia
Received: 31 Oct 2016 – Accepted: 12 Dec 2016 – Published: 13 Dec 2016
Abstract. Deriving absorption coefficients from Aethalometer attenuation data requires different corrections to compensate for artifacts related to filter-loading effects, scattering by filter fibers, and scattering by aerosol particles. In this study, two different correction schemes were applied to 7-wavelength Aethalometer data, using Multi-Angle Absorption Photometer (MAAP) data as a reference absorption measurement at 637 nm. The compensation algorithms were compared to 5-wavelength offline absorption measurements obtained with a Multi-Wavelength Absorbance Analyzer (MWAA), which serves as a multiple-wavelength reference measurement. The online measurements took place in the Amazon rainforest, from the wet-to-dry transition season to the dry season (June–September 2014). The mean absorption coefficient (at 637 nm) during this period was 1.8 ± 2.1 Mm−1, with a maximum of 15.9 Mm−1. Under these conditions, the filter-loading compensation was negligible. One of the correction schemes was found to artificially increase the short-wavelength absorption coefficients. It was found that accounting for the aerosol optical properties in the scattering compensation significantly affects the absorption Ångström exponent (AAE) retrievals. Proper Aethalometer data compensation schemes are crucial to retrieve the correct AAE, which is commonly implemented in brown carbon contribution calculations. We found that a "hybrid" algorithm was more appropriate to achieve optimal correlations with the MAAP absorption coefficients and with the AAE retrieved from offline MWAA measurements.
Saturno, J., Pöhlker, C., Massabò, D., Brito, J., Carbone, S., Cheng, Y., Chi, X., Ditas, F., Hrabě de Angelis, I., Morán-Zuloaga, D., Pöhlker, M. L., Rizzo, L. V., Walter, D., Wang, Q., Artaxo, P., Prati, P., and Andreae, M. O.: Comparison of different Aethalometer correction schemes and a reference multi-wavelength absorption technique for ambient aerosol data, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-361, in review, 2016.