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Please use this identifier to cite or link to this item: http://apo.ansto.gov.au/dspace/handle/10238/9194

Title: Radon: a universal baseline indicator at sites with contrasting physical settings
Authors: Chambers, SD
Williams, AG
Giemsa, E
Labuschagne, C
Conen, F
Reimann, S
Krummel, PB
Steele, LP
Barnes, JE
Keywords: Meteorology
Atmospheres
Chemical composition
Earth astmosphere
Air
Data analysis
Tracer techniques
Air pollution
Radon
Wind
ANSTO
Issue Date: 16-Nov-2016
Publisher: Bureau of Meteorology and CSIRO Oceans and Atmosphere, Climate Science Centre.
Citation: Chambers, S. D., Williams, A. G., Giemsa, E., Labuschagne, C., Conen, F., Reimann, S., Krummel, P.B., Steele, L. P. & Barnes, J. E. (2016). Radon: a universal baseline indicator at sites with contrasting physical settings. Paper presented at the Atmospheric Composition & Chemistry Observations & Modelling Conference incorporating the Cape Grim Annual Science Meeting 2016, Stanley, Tasmania.
Abstract: The primary goal of World Meteorological Organisation Global Atmosphere Watch (WMO‐GAW) baseline stations is systematic global monitoring of chemical composition of the atmosphere, requiring a reliable, consistent and unambiguous approach for the identification of baseline air. Premier stations in the GAW baseline network span a broad range of physical settings, from remote marine to high‐altitude continental sites, necessitating carefully tailored site‐specific requirements for baseline sampling, data selection, and analysis. Radon‐222 is a versatile and unambiguous terrestrial tracer, widely‐used in transport and mixing studies. Since the majority of anthropogenic pollution sources also have terrestrial origins, radon has become a popular addition to the ‘baseline selection toolkit’ at numerous GAW stations as a proxy for ‘pollution potential’. In the past, detector performance and postprocessing methods necessitated the adoption of a relaxed (e.g. 100 mBq m‐3) radon threshold for minimal terrestrial influence, intended to be used in conjunction with other baseline criteria and analysis procedures, including wind speed, wind direction, particle number, outlier rejection and filtering. However, recent improvements in detector sensitivity, stability and post‐processing procedures have reduced detection limits below 10 mBq m‐3 at Cape Grim and to 25 mBq m‐3 at other baseline stations. Consequently, for suitably sensitive instruments (such as the ANSTO designed and built two‐filter dual‐flow‐loop detectors), radon concentrations alone can be used to unambiguously identify air masses that have been removed from terrestrial sources (at altitude or over ice), or in equilibrium with the ocean surface, for periods of >2‐3 weeks (radon ≤ 40 mBq m‐3). Potentially, radon observations alone can thus provide a consistent and universal (site independent) means for baseline identification. Furthermore, for continental sites with complex topography and meteorology, where true ‘baseline’ conditions may never occur, radon can be used to indicate the least terrestrially‐perturbed air masses, and provide a means by which to apply limits to the level of ‘acceptable terrestrial influence’ for a given application. We demonstrate the efficacy of the radon‐based selection at a range of sites in contrasting physical settings, including: Cape Grim (Tasmania), Cape Point (South Africa), Mauna Loa (Hawaii), Jungfraujoch (Switzerland) and Schneefernerhaus (Germany).
URI: http://apo.ansto.gov.au/dspace/handle/10238/9194
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