Articles | Volume 10, issue 8
Atmos. Meas. Tech., 10, 2837–2850, 2017
Atmos. Meas. Tech., 10, 2837–2850, 2017

Research article 09 Aug 2017

Research article | 09 Aug 2017

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. Andreae1,8,9 Jorge Saturno et al.
  • 1Biogeochemistry and Multiphase Chemistry Departments, Max Planck Institute for Chemistry, P.O. Box 3060, 55020 Mainz, Germany
  • 2Department of Physics & INFN, University of Genoa, via Dodecaneso 33, 16146, Genoa, 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, Nanjing, 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

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 seven-wavelength Aethalometer data, using multi-angle absorption photometer (MAAP) data as a reference absorption measurement at 637 nm. The compensation algorithms were compared to five-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 (åABS) retrievals. Proper Aethalometer data compensation schemes are crucial to retrieve the correct åABS, which is commonly implemented in brown carbon contribution calculations. Additionally, we found that the wavelength dependence of uncompensated Aethalometer attenuation data significantly correlates with the åABS retrieved from offline MWAA measurements.

Short summary
Different Aethalometer correction schemes were compared to a multi-wavelength absorption reference measurement. One of the correction schemes was found to artificially increase the short-wavelength absorption coefficients. It was found that accounting for aerosol scattering properties in the correction is crucial to retrieve the proper absorption Ångström exponent (AAE). We found that the raw AAE of uncompensated Aethalometer attenuation significantly correlates with a measured reference AAE.