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

M. A. Burgos; M. A. Burgos; E. Andrews; G. Titos; A. Benedetti; H. Bian; H. Bian; V. Buchard; V. Buchard; G. Curci; G. Curci; Z. Kipling; A. Kirkevåg; H. Kokkola; A. Laakso; J. Letertre-Danczak; M. T. Lund; H. Matsui; G. Myhre; C. Randles; M. Schulz; T. van Noije; K. Zhang; L. Alados-Arboledas; U. Baltensperger; A. Jefferson; J. Sherman; J. Sun; E. Weingartner; E. Weingartner; P. Zieger; P. Zieger

doi:10.5194/acp-20-10231-2020

Atmospheric Chemistry and Physics (Sep 2020)

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

M. A. Burgos,
M. A. Burgos,
E. Andrews,
G. Titos,
A. Benedetti,
H. Bian,
H. Bian,
V. Buchard,
V. Buchard,
G. Curci,
G. Curci,
Z. Kipling,
A. Kirkevåg,
H. Kokkola,
A. Laakso,
J. Letertre-Danczak,
M. T. Lund,
H. Matsui,
G. Myhre,
C. Randles,
M. Schulz,
T. van Noije,
K. Zhang,
L. Alados-Arboledas,
U. Baltensperger,
A. Jefferson,
J. Sherman,
J. Sun,
E. Weingartner,
E. Weingartner,
P. Zieger,
P. Zieger

Affiliations

M. A. Burgos: Department of Environmental Science, Stockholm University, Stockholm, Sweden
M. A. Burgos: Bolin Centre for Climate Research, Stockholm, Sweden
E. Andrews: Cooperative Institute for Research in Environmental Studies, University of Colorado, Boulder, Colorado, USA
G. Titos: Andalusian Institute for Earth System Research, University of Granada, Granada, Spain
A. Benedetti: European Centre for Medium-Range Weather Forecasts, Reading, UK
H. Bian: NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA
H. Bian: Joint Center for Earth Systems Technology, University of Maryland, Baltimore County, Maryland, USA
V. Buchard: NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA
V. Buchard: GESTAR/Universities Space Research Association, Columbia, Maryland, USA
G. Curci: Dipartimento di Scienze Fisiche e Chimiche, Università degli Studi dell'Aquila, L'Aquila, Italy
G. Curci: Centre of Excellence CETEMPS, Università degli Studi dell'Aquila, L'Aquila, Italy
Z. Kipling: European Centre for Medium-Range Weather Forecasts, Reading, UK
A. Kirkevåg: Research Department, Norwegian Meteorological Institute, Oslo, Norway
H. Kokkola: Finnish Meteorological Institute, Atmospheric Research Centre of Eastern Finland, Kuopio, Finland
A. Laakso: Finnish Meteorological Institute, Atmospheric Research Centre of Eastern Finland, Kuopio, Finland
J. Letertre-Danczak: European Centre for Medium-Range Weather Forecasts, Reading, UK
M. T. Lund: Center for International Climate Research, Oslo, Norway
H. Matsui: Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
G. Myhre: Center for International Climate Research, Oslo, Norway
C. Randles: NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA
M. Schulz: Research Department, Norwegian Meteorological Institute, Oslo, Norway
T. van Noije: Royal Netherlands Meteorological Institute, De Bilt, the Netherlands
K. Zhang: Earth Systems Analysis and Modeling, Pacific Northwest National Laboratory, Richland, Washington, USA
L. Alados-Arboledas: Andalusian Institute for Earth System Research, University of Granada, Granada, Spain
U. Baltensperger: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland
A. Jefferson: Cooperative Institute for Research in Environmental Studies, University of Colorado, Boulder, Colorado, USA
J. Sherman: Department of Physics and Astronomy, Appalachian State University, Boone, North Carolina, USA
J. Sun: Key Laboratory of Atmospheric Chemistry of CMA, Chinese Academy of Meteorological Sciences, Beijing 100081, China
E. Weingartner: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland
E. Weingartner: now at: Institute for Sensing and Electronics, University of Applied Sciences, Windisch, Switzerland
P. Zieger: Department of Environmental Science, Stockholm University, Stockholm, Sweden
P. Zieger: Bolin Centre for Climate Research, Stockholm, Sweden

DOI: https://doi.org/10.5194/acp-20-10231-2020
Journal volume & issue: Vol. 20
pp. 10231 – 10258

Abstract

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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. Based on our evaluation of sea salt scattering enhancement and simulated organic mass fraction, there is a strong indication that differences in the model parameterizations of hygroscopicity and model chemistry are driving at least some of the observed diversity in simulated f(RH). Additionally, a key point is that defining dry conditions is difficult from an observational point of view and, depending on the aerosol, may influence the measured f(RH). The definition of dry also impacts our model evaluation, because several models exhibit significant water uptake between RH = 0 % and 40 %. The multisite average ratio between model outputs and measurements is 1.64 when RH = 0 % is assumed as the model dry RH and 1.16 when RH = 40 % is the model dry RH value. 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). This will be particularly relevant when a location is dominated by a deliquescent aerosol such as sea salt. 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. Recommendations for future model–measurement evaluation and model improvements are provided.

Published in Atmospheric Chemistry and Physics

ISSN: 1680-7316 (Print); 1680-7324 (Online)
Publisher: Copernicus Publications
Country of publisher: Germany
LCC subjects: Science: Physics; Science: Chemistry
Website: http://www.atmospheric-chemistry-and-physics.net/

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