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Discussion papers
https://doi.org/10.5194/acp-2019-1190
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-1190
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 20 Jan 2020

Submitted as: research article | 20 Jan 2020

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This preprint is currently under review for the journal ACP.

A global model-measurement evaluation of particle light scattering coefficients at elevated relative humidity

María A. Burgos1,2, Elisabeth J. Andrews3, Gloria Titos4, Angela Benedetti5, Huisheng Bian6,7, Virginie Buchard6,8, Gabriele Curci9,10, Alf Kirkevåg11, Harri Kokkola12, Anton Laakso12, Marianne T. Lund13, Hitoshi Matsui14, Gunnar Myhre13, Cynthia Randles6, Michael Schulz11, Twan van Noije15, Kai Zhang16, Lucas Alados-Arboledas4, Urs Baltensperger17, Anne Jefferson3, James Sherman18, Junying Sun19, Ernest Weingartner17,a, and Paul Zieger1,2 María A. Burgos et al.
  • 1Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, Sweden
  • 2Bolin Centre for Climate Research, Stockholm, Sweden
  • 3Cooperative Institute for Research in Environmental Studies, University of Colorado, Boulder, USA
  • 4Andalusian Institute for Earth System Research, University of Granada, Granada, Spain
  • 5European Centre for Medium-Range Weather Forecasts, Reading, UK
  • 6NASA/Goddard Space Flight Center, USA
  • 7University of Maryland Baltimore County, Maryland, USA
  • 8GESTAR/Universities Space Research Association, Columbia, USA
  • 9Dipartimento di Scienze Fisiche e Chimiche, Universita' degli Studi dell'Aquila, L'Aquila, Italy
  • 10Centre of Excellence CETEMPS, Università degli Studi dell'Aquila, L'Aquila, Italy
  • 11Norwegian Meteorological Institute, Oslo, Norway
  • 12Finnish Meteorological Institute, Kuopio, Finland
  • 13Center for International Climate Research, Oslo, Norway
  • 14Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
  • 15Royal Netherlands Meteorological Institute, De Bilt, the Netherlands
  • 16Earth Systems Analysis and Modeling, Pacific Northwest National Laboratory, Richland, WA, USA
  • 17Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland
  • 18Department of Physics and Astronomy, Appalachian State University, Boone, USA
  • 19Key Laboratory of Atmospheric Chemistry of CMA, Chinese Academy of Meteorological Sciences, Beijing 100081, China
  • anow at: Institute for Sensing and Electronics, University of Applied Sciences, Windisch, Switzerland

Abstract. The uptake of water by atmospheric aerosols has a pronounced effect on particle light scattering properties which in turn are strongly dependent on the ambient relative humidity (RH). Earth system models need to account for the aerosol water uptake and its influence on light scattering in order to properly capture the overall radiative effects of aerosols. Here we present a comprehensive model-measurement evaluation of the particle light scattering enhancement factor f(RH), defined as the particle light scattering coefficient at elevated RH (here set to 85 %) divided by its dry value. The comparison uses simulations from 10 Earth system models and a global dataset of surface-based in situ measurements. In general, we find a large diversity in the magnitude of predicted f(RH) amongst the different models which can not be explained by the site types. There is strong indication that differences in the model parameterizations of hygroscopicity and perhaps mixing state are driving at least some of the observed diversity in simulated f(RH). An important finding is that the models show a significantly larger discrepancy with the observations if RHref = 0 % is chosen as the model reference RH compared to when RHref = 40 % is used. The multi-site average ratio between model outputs and measurements is 1.64 in the former case and 1.16 in the latter. The overestimation by the models is believed to originate from the hygroscopicity parameterizations at the lower RH range which may not implement all phenomena taking place (i.e. not fully dried particles and hysteresis effects). Our results emphasize the need to consider the measurement conditions in such comparisons and recognize that measurements referred to as dry may not be dry in model terms.

María A. Burgos et al.

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Time series of aerosol light scattering coefficients and enhancement factors from humidified tandem nephelometers at twenty-six stations between 1998 and 2017 M. A. Burgos, E. Andrews, G. Titos, L. Alados-Arboledas, U. Baltensperger, D. Day, A. Jefferson, N. Kalivitis, N. Mihalopoulos, J. Sherman, J. Sun, E. Weingartner, and P. Zieger https://doi.org/10.21336/gen.4

María A. Burgos et al.

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Short summary
We investigate how well models represent the enhancement in scattering coefficients due to particle water uptake, and perform an evaluation of several implementation schemes used in ten earth system models. Our results show a general overestimation of modeled scattering enhancement. More work is needed to understand how to parameterize water uptake at low RH (RH = 0–40 %). Model dry conditions may differ from the measurement ones, this should be considered in model/measurement comparisons.
We investigate how well models represent the enhancement in scattering coefficients due to...
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