Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 5.509 IF 5.509
  • IF 5-year value: 5.689 IF 5-year 5.689
  • CiteScore value: 5.44 CiteScore 5.44
  • SNIP value: 1.519 SNIP 1.519
  • SJR value: 3.032 SJR 3.032
  • IPP value: 5.37 IPP 5.37
  • h5-index value: 86 h5-index 86
  • Scimago H index value: 161 Scimago H index 161
Volume 16, issue 5 | Copyright
Atmos. Chem. Phys., 16, 3525-3561, 2016
https://doi.org/10.5194/acp-16-3525-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 17 Mar 2016

Research article | 17 Mar 2016

Evaluation of observed and modelled aerosol lifetimes using radioactive tracers of opportunity and an ensemble of 19 global models

N. I. Kristiansen1, A. Stohl1, D. J. L. Olivié2, B. Croft3, O. A. Søvde4, H. Klein2, T. Christoudias5, D. Kunkel6, S. J. Leadbetter7, Y. H. Lee8, K. Zhang9, K. Tsigaridis10, T. Bergman11, N. Evangeliou1,12, H. Wang9, P.-L. Ma9, R. C. Easter9, P. J. Rasch9, X. Liu13, G. Pitari14, G. Di Genova14, S. Y. Zhao15, Y. Balkanski12, S. E. Bauer10, G. S. Faluvegi10, H. Kokkola11, R. V. Martin3, J. R. Pierce16,3, M. Schulz2, D. Shindell8, H. Tost6, and H. Zhang15 N. I. Kristiansen et al.
  • 1NILU – Norwegian Institute for Air Research, Kjeller, Norway
  • 2Norwegian Meteorological Institute, Oslo, Norway
  • 3Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada
  • 4Center for International Climate and Environmental Research – Oslo (CICERO), Oslo, Norway
  • 5The Cyprus Institute, Nicosia, Cyprus
  • 6Institute for Atmospheric Physics, Johannes Gutenberg University of Mainz, Mainz, Germany
  • 7Met Office, Exeter, UK
  • 8Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC, USA
  • 9Pacific Northwest National Laboratory (PNNL), Richland, WA, USA
  • 10Center for Climate Systems Research, Columbia University, and NASA Goddard Institute for Space Studies, New York, NY, USA
  • 11Finnish Meteorological Institute, Kuopio, Finland
  • 12Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, Gif-sur-Yvette, France
  • 13Department of Atmospheric Science, University of Wyoming, Laramie, WY, USA
  • 14University of L'Aquila, L'Aquila, Italy
  • 15Laboratory for Climate Studies, National Climate Center, Chinese Meteorological Administration, Beijing, China
  • 16Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA

Abstract. Aerosols have important impacts on air quality and climate, but the processes affecting their removal from the atmosphere are not fully understood and are poorly constrained by observations. This makes modelled aerosol lifetimes uncertain. In this study, we make use of an observational constraint on aerosol lifetimes provided by radionuclide measurements and investigate the causes of differences within a set of global models. During the Fukushima Dai-Ichi nuclear power plant accident of March 2011, the radioactive isotopes cesium-137 (137Cs) and xenon-133 (133Xe) were released in large quantities. Cesium attached to particles in the ambient air, approximately according to their available aerosol surface area. 137Cs size distribution measurements taken close to the power plant suggested that accumulation-mode (AM) sulfate aerosols were the main carriers of cesium. Hence, 137Cs can be used as a proxy tracer for the AM sulfate aerosol's fate in the atmosphere. In contrast, the noble gas 133Xe behaves almost like a passive transport tracer. Global surface measurements of the two radioactive isotopes taken over several months after the release allow the derivation of a lifetime of the carrier aerosol. We compare this to the lifetimes simulated by 19 different atmospheric transport models initialized with identical emissions of 137Cs that were assigned to an aerosol tracer with each model's default properties of AM sulfate, and 133Xe emissions that were assigned to a passive tracer. We investigate to what extent the modelled sulfate tracer can reproduce the measurements, especially with respect to the observed loss of aerosol mass with time. Modelled 137Cs and 133Xe concentrations sampled at the same location and times as station measurements allow a direct comparison between measured and modelled aerosol lifetime. The e-folding lifetime τe, calculated from station measurement data taken between 2 and 9 weeks after the start of the emissions, is 14.3 days (95 % confidence interval 13.1–15.7 days). The equivalent modelled τe lifetimes have a large spread, varying between 4.8 and 26.7 days with a model median of 9.4 ± 2.3 days, indicating too fast a removal in most models. Because sufficient measurement data were only available from about 2 weeks after the release, the estimated lifetimes apply to aerosols that have undergone long-range transport, i.e. not for freshly emitted aerosol. However, modelled instantaneous lifetimes show that the initial removal in the first 2 weeks was quicker (lifetimes between 1 and 5 days) due to the emissions occurring at low altitudes and co-location of the fresh plume with strong precipitation. Deviations between measured and modelled aerosol lifetimes are largest for the northernmost stations and at later time periods, suggesting that models do not transport enough of the aerosol towards the Arctic. The models underestimate passive tracer (133Xe) concentrations in the Arctic as well but to a smaller extent than for the aerosol (137Cs) tracer. This indicates that in addition to too fast an aerosol removal in the models, errors in simulated atmospheric transport towards the Arctic in most models also contribute to the underestimation of the Arctic aerosol concentrations.

Download & links
Publications Copernicus
Download
Short summary
Processes affecting aerosol removal from the atmosphere are not fully understood. In this study we investigate to what extent atmospheric transport models can reproduce observed loss of aerosols. We compare measurements of radioactive isotopes, that attached to ambient sulfate aerosols during the 2011 Fukushima nuclear accident, to 19 models using identical emissions. Results indicate aerosol removal that is too fast in most models, and apply to aerosols that have undergone long-range transport.
Processes affecting aerosol removal from the atmosphere are not fully understood. In this study...
Citation
Share