Map of radon flux at the Australian land surface.

A time-dependent map of radon-222 flux density at the Australian land surface has been constructed with a spatial resolution of 0.05° and temporal resolution of one month. Radon flux density was calculated from a simple model utilising data from national gamma-ray aerial surveys, modelled soil moisture, and maps of soil properties. The model was calibrated against a large data set of accumulation-chamber measurements, thereby constraining it with experimental data. A notable application of the map is in atmospheric mixing and transport studies which use radon as a tracer, where it is a clear improvement on the common assumption of uniform radon flux density. © Author(s) 201

Receptor modelling with PMF2 and ME2 using aerosol data from Hong Kong.

A number of techniques, such as principal component analysis and factor analysis, have been used in receptor modelling where measured aerosol composition at the sampling site are analysed in order to determine the likely source contributions. In this study factor analysis with nonnegative factor elements has been carried out using two techniques as implemented in the PMF2 and ME2 computer codes. The various analysis techniques provided by the two programs are illustrated using measured data at Hong Kong as a case study, which covers a period of three years (2001 to 2003). Both analysis techniques resulted in similar results which are presented in this report. Data bootstrapping was also carried out as an additional check on the quality of the results

Influence of turbulent mixing and air circulation in the lower atmosphere on fetch areas of selected WMO Global Atmosphere Watch baseline air pollution stations.

The World Meteorological Organisation (WMO) established the Global Atmosphere Watch (GAW) Programme in 1989. The scientific goals of GAW relate to investigating the role of atmospheric chemistry in global climate change, and include: understanding the complex mechanisms with respect to natural and anthropogenic atmospheric change; and improving the understanding of interactions between the atmosphere, ocean, and biosphere.American Meteorological Society; Stockholm Universit

222Rn calibrated mercury fluxes from terrestrial surfaces of southern Africa derived from observations at Cape Point, South Africa

Gaseous elemental mercury (GEM) and 222Rn, a radioactive gas of primarily terrestrial origin with a half-life of 3.8 days, have been measured simultaneously at Cape Point, South Africa, since March 2007. Between March 2007 and December 2009 altogether 59 events with high 222Rn concentrations were identified. GEM correlated with 222Rn in 41 of the events and was constant during the remaining events without significant correlation. The average GEM/222Rn emission ratio of all events was -0.0047 ± 0.0054 pg mBq-1, with ± 0.0054 being the standard error of the average. With an emission rate of 1.1 222Rn atoms cm-2 s-1 and a correction for the transport duration, this emission ratio corresponds to a radon calibrated flux of about -0.53 ± 0.62 ng m-2 h-1 which is statistically not distinguishable from zero. With wet deposition, which is not included in this estimate, the terrestrial surface of southern Africa appears to be a net mercury sink. © Owned by the authors, published by EDP Sciences, 201

222Rn-calibrated mercury fluxes from terrestrial surface of southern Africa

Gaseous elemental mercury (GEM) and 222Rn, a radioactive gas of primarily terrestrial origin with a half-life of 3.8 days, have been measured simultaneously at Cape Point, South Africa, since March 2007. Between March 2007 and December 2011, altogether 191 events with high 222Rn concentrations were identified. GEM correlated with 222Rn in 94 of the events and was constant during almost all the remaining events without significant correlation. The average GEM / 222Rn flux ratio of all events including the non-significant ones was −0.0001 with a standard error of ±0.0030 pg mBq−1. Weighted with the event duration, the average GEM / 222Rn flux ratio was −0.0048 ± 0.0011 pg mBq−1. With an emission rate of 1.1 222Rn atoms cm−2 s−1 and a correction for the transport time, this flux ratio corresponds to a radon-calibrated flux of about −0.54 ng GEM m−2 h−1 with a standard error of ±0.13 ng GEM m−2 h−1 (n = 191). With wet deposition, which is not included in this estimate, the terrestrial surface of southern Africa seems to be a net mercury sink of about −1.55 ng m−2 h−1. The additional contribution of an unknown but presumably significant deposition of reactive gaseous mercury would further increase this sink.© 2013, European Geosciences Unio

The vertical distribution of radon in clear and cloudy daytime terrestrial boundary layers

Radon ((222)Rn) is a powerful natural tracer of mixing and exchange processes in the atmospheric boundary layer. The authors present and discuss the main features of a unique dataset of 50 high-resolution vertical radon profiles up to 3500 m above ground level, obtained in clear and cloudy daytime terrestrial boundary layers over an inland rural site in Australia using an instrumented motorized research glider. It is demonstrated that boundary layer radon profiles frequently exhibit a complex layered structure as a result of mixing and exchange processes of varying strengths and extents working in clear and cloudy conditions within the context of the diurnal cycle and the synoptic meteorology. Normalized aircraft radon measurements are presented, revealing the characteristic structure and variability of three major classes of daytime boundary layer: 1) dry convective boundary layers, 2) mixed layers topped with residual layers, and 3) convective boundary layers topped with coupled nonprecipitating clouds. Robust and unambiguous signatures of important atmospheric processes in the boundary layer are identifiable in the radon profiles, including "top-down" mixing associated with entrainment in clear-sky cases and strongly enhanced venting and subcloud-layer mixing when substantial active cumulus are present. In poorly mixed conditions, radon gradients in the daytime atmospheric surface layer significantly exceed those predicted by Monin-Obukhov similarity theory. In two case studies, it is demonstrated for the first time that a sequence of vertical radon profiles measured over the course of a single day can consistently reproduce major structural features of the evolving boundary layer.© 2011, American Meteorological Society

Constraining annual and seasonal radon-222 flux density from the Southern Ocean using radon-222 concentrations in the boundary layer at Cape Grim

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

Evaluating radon-derived mixing depth as a potential length scale for nocturnal mixing processes over land.

To evaluate, and ultimately improve, numerical schemes for vertical mixing and exchange within the atmospheric boundary layer, and in particular the nocturnal boundary layer, it is necessary to quantify mixing processes within the lower atmosphere at a temporal resolution sufficient to resolve the diurnal cycle. One way to quantitatively characterize near-surface mixing on diurnal time scales is to make continuous, high temporal resolution vertical gradient measurements of a suitable atmospheric tracer. Radon-222 (radon) is a naturally occurring, radioactive, noble gas that is poorly soluble in water. It has a relatively uniform terrestrial source function and its only significant atmospheric sink is radioactive decay. Radon’s 3.8-day half-life is also ideal for atmospheric boundary layer mixing studies, being much larger than turbulent timescales (<1 hour) but short enough to ensure typical concentrations in the free troposphere are orders of magnitude lower than near surface concentrations. Under strongly stable conditions, when the nocturnal mixing depth can become too shallow to be resolved by SODAR or LIDAR, nearsurface radon concentrations remain intimately linked to the local mixing depth. Radon gradient measurements between 2 and 50 m have been collected for more than a year from a 50 m tower near Sydney, Australia, using a pair of 1500 L dual flow loop, two filter radon detectors, with a lower limit of detection of approximately 40 mBq m-3. The site is topographically complex and, being less than 20 km from the coast, is also subjected to marine influences. While the magnitude of the diurnal radon signal at Lucas Heights is suppressed compared to that of flat, inland sites, a clear correlation is observed between the measured radon gradients and the strength of mechanical and/or convective turbulence. On windy nights (wind speeds in excess of 2 ms-1, or Bulk Richardson number less 0.25), the 2 – 50 m radon gradient rarely exceeds 1 Bq m-3. However, on strongly stable nights (clear skies with wind speeds < 2 ms-1), when the mixing depth is small and sometimes even below 50 m (so that the upper tower level is above the stable boundary layer), large radon gradients are observed that can exceed 5 Bq m-3. On stable nights it is possible to estimate the nocturnal mixing depth using a simple depth-integrated radon budget equation. The present investigation focuses on whether these mixing depth estimates could be useful as a length scale for investigations of nocturnal mixing processes. Initial comparisons with nocturnal mixing depths derived from simulations using the regional LAPS model provided by the Australian Bureau of Meteorology have been encouraging, considering the local terrain variability.European Geosciences Unio