Towards a universal “baseline” characterisation of air masses for high- and low-altitude observing stations using Radon-222
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Date
2015-07-30
Journal Title
Journal ISSN
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Publisher
Taiwan Association for Aerosol Research
Abstract
We demonstrate the ability of atmospheric radon concentrations to reliably and unambiguously identify local and
remote terrestrial influences on an air mass, and thereby the potential for alteration of trace gas composition by
anthropogenic and biogenic processes. Based on high accuracy (lower limit of detection 10–40 mBq m–3), high temporal
resolution (hourly) measurements of atmospheric radon concentration we describe, apply and evaluate a simple two-step
method for identifying and characterising constituent mole fractions in baseline air. The technique involves selecting a
radon-based threshold concentration to identify the “cleanest” (least terrestrially influenced) air masses, and then
performing an outlier removal step based on the distribution of constituent mole fractions in the identified clean air
masses. The efficacy of this baseline selection technique is tested at three contrasting WMO GAW stations: Cape Grim (a
coastal low-altitude site), Mauna Loa (a remote high-altitude island site), and Jungfraujoch (a continental high-altitude
site). At Cape Grim and Mauna Loa the two-step method is at least as effective as more complicated methods employed to
characterise baseline conditions, some involving up to nine steps. While it is demonstrated that Jungfraujoch air masses
rarely meet the baseline criteria of the more remote sites, a selection method based on a variable monthly radon threshold
is shown to produce credible “near baseline” characteristics. The seasonal peak-to-peak amplitude of recent monthly
baseline CO2 mole fraction deviations from the long-term trend at Cape Grim, Mauna Loa and Jungfraujoch are estimated
to be 1.1, 6.0 and 8.1 ppm, respectively. © Taiwan Association for Aerosol Research
Description
Keywords
Air, Baseline ecology, Radon 222, Greenhouse gases, Radon, Mountains
Citation
Chambers, S. D., Williams, A. G., Conen, F., Griffiths, A. D., Reimann, S., Steinbacher, M., Krummel, P. B., Steele, L. P., van der Schoot, M. V., Galbally, I. E., Molloy, S. B., & Barnes, J. E. (2015). Towards a universal “baseline” characterisation of air masses for high- and low-altitude observing stations using radon-222. Aerosol and Air Quality Research, 16(3), 885-899. doi:10.4209/aaqr.2015.06.0391