Constraining annual and seasonal radon-222 flux density from the Southern Ocean using radon-222 concentrations in the boundary layer at Cape Grim
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Date
2013-02-14
Journal Title
Journal ISSN
Volume Title
Publisher
Taylor & Francis Group
Abstract
Radon concentrations measured between 2001 and 2008 in marine air at Cape Grim, a baseline site in northwestern Tasmania, are used to constrain the radon flux density from the Southern Ocean. A method is
described for selecting hourly radon concentrations that are least perturbed by land emissions and dilution by
the free troposphere. The distribution of subsequent radon flux density estimates is representative of a large
area of the Southern Ocean, an important fetch region for Southern Hemisphere climate and air pollution
studies. The annual mean flux density (0.27 mBq m 2 s 1) compares well with the mean of the limited number
of spot measurements previously conducted in the Southern Ocean (0.24 mBq m 2 s 1), and to some spot
measurements made in other oceanic regions. However, a number of spot measurements in other oceanic regions, as well as most oceanic radon flux density values assumed for modelling studies and intercomparisons,
are considerably lower than the mean reported here. The reported radon flux varies with seasons and, in summer, with latitude. It also shows a quadratic dependence on wind speed and significant wave height, as postulated and measured by others, which seems to support our assumption that the selected least perturbed
radon concentrations were in equilibrium with the oceanic radon source. By comparing the least perturbed radon observations in 2002 2003 with corresponding ‘TransCom’ model intercomparison results, the best
agreement is found when assuming a normally distributed radon flux density with s 0.075 mBq m 2 s 1. © 2013, W. Zahorowski et al.
Description
Keywords
Radon, Seas, Tasmania, Flux density, Troposphere, Wind
Citation
Zahorowski, W., Griffiths, A. D., Chambers, S. D., Williams, A. G., Law, R. M., Crawford, J., & Werczynski, S. (2013). Constraining annual and seasonal radon-222 flux density from the Southern Ocean using radon-222 concentrations in the boundary layer at Cape Grim. Tellus B:
Chemical and Physical Meteorology, 65(1), 19622. doi:10.3402/tellusb.v65i0.19622