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

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

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

Improved estimation of total boundary layer radon for budget studies and regional integrations.

Estimation of the total amount of the natural radioactive tracer radon-222 (radon) in a vertical column through the troposphere is a critical step in the process of calculating regionally integrated emissions of important greenhouse gases using radon-calibrated budget techniques. As continuous long-term radon time series used for such calculations are typically gathered at sites located at or near the surface, a rigorous column radon estimate would require knowledge of the vertical distribution of radon through the atmospheric boundary layer (ABL). The most frequent approach to addressing this issue is to assume a uniform radon profile within the ABL, and no radon in the free atmosphere above. This study aims at refining these traditional assumptions by presenting vertical integrations of high-resolution radon profiles, gathered using a motorised glider in and above daytime boundary layers over rural inland Australia under a range of stability and cloud conditions. On cloudless days, a large drop in radon concentrations across the inversion is evident from the vertical radon profiles. This is a result of radon depletion in the free atmosphere by radioactive decay (radon’s half-life is 3.8 days), and the “top-down” diffusion process associated with entrainment of this radon-depleted air into the ABL results in a range of radon gradients observed in the upper part of the mixed layer. When actively coupled boundary layer clouds are present, the profiles indicate strongly enhanced vertical mixing and venting of radon from the sub-cloud layer into the cloud layer. Under these conditions, the proportion of total-column radon remaining in the sub-cloud layer can sometimes be as low as 30%. Based on the enhanced understanding of vertical radon distributions in daytime terrestrial boundary layers gained from these airborne studies, refinements are suggested to the traditional estimation of total column radon from datasets where only surface-based radon measurements are available. These refinements are shown to result in improved estimates of total boundary layer radon in both clear and cloudy conditions.European Geosciences Unio

Biking for research [website]

Radon is an excellent tracer of other gases because it is unreactive and its short half-life (3.8 days) prevents any significant build-up in the atmosphere over long time scales. The KNMI (Royal Netherlands Meteorological Institute) Cabauw Experimental Site for Atmospheric Research with its 213m meteorological tower has been a focus of experimental boundary layer research since the 1970s. Over the years, the site has expanded the scope of its research applications to include land-atmosphere interactions. In 2006 and 2007, ANSTO designed and built two 1500L detectors for 222Rn radon observations which were installed on the Cabauw tower, drawing air from 200m and 20m AGL, respectively. These observations are an important part of a larger program to characterise regional emissions of greenhouse gases and other pollutants, to evaluate the performance of climate and atmospheric transport models, and to quantify turbulent mixing processes in the lower atmosphere. Radon gas is emitted naturally from soils, where it is formed by radioactive transformation of 226Ra radium as part of the decay chain of primordial 238U uranium in the earth’s crust. The strength of radon emissions from the land surface into the atmosphere depends on the soil mineralogy and porosity, and to a lesser extent also varies with changes in atmospheric pressure and soil moisture. As the oceanic radon flux is effectively negligible (at least 100 times smaller than that from land), significant radon concentrations measured in air samples indicate that the air mass has been in contact with land within the previous few weeks. The use of radon as a tracer in atmospheric and climate research is limited by large uncertainties in the magnitude and distribution of the radon flux density over the Earth’s surface. Maps of radon emissions have previously been generated by assigning a constant value to large geographical areas (sometimes reducing at high latitudes according to known changes in snow and ice coverage), or from aerial surveys using terrestrial gamma radiation as a proxy. The only direct method of measuring radon exhalation from soil is by using an accumulation chamber. Such measurements are rare, and the new ANSTO designed and built radon emanometer has been uniquely designed with this purpose in mind. The ANSTO portable accumulation chamber allows radon to accumulate in a chamber placed over the soil. The evolution of the measured radon concentration within the chamber is continuously monitored, and the surface flux at that location can then be estimated after a given time period from the integrated measurements. Equipped with the ANSTO portable emanometer, a shovel, GPS locator, soil type maps of the area and the soil moisture probe, Sylvester Werczynski moved around the Cabauw tower on a three-wheeled pushbike that he hired locally. “The pushbike was actually the most practical means to access the various measurement locations, as the survey area consisted of a network of flat green polders with thousands of canals, windmills and farm houses - a typical country landscape in the Netherlands,” says Werczynski. - See more at: http://www.ansto.gov.au/AboutANSTO/MediaCentre/News/ACS049714#sthash.thIt2IZi.dpu

Increasing the accuracy and temporal resolution of two-filter radon–222 measurements by correcting for the instrument response

Dual-flow-loop two-filter radon detectors have a slow time response, which can affect the interpretation of their output when making continuous observations of near-surface atmospheric radon concentrations. While concentrations are routinely reported hourly, a calibrated model of detector performance shows that ∼ 40 % of the signal arrives more than an hour after a radon pulse is delivered. After investigating several possible ways to correct for the detector's slow time response, we show that a Bayesian approach using a Markov chain Monte Carlo sampler is an effective method. After deconvolution, the detector's output is redistributed into the appropriate counting interval and a 10 min temporal resolution can be achieved under test conditions when the radon concentration is controlled. In the case of existing archived observations, collected under less ideal conditions, the data can be retrospectively reprocessed at 30 min resolution. In one case study, we demonstrate that a deconvolved radon time series was consistent with the following: measurements from a fast-response carbon dioxide monitor; grab samples from an aircraft; and a simple mixing height model. In another case study, during a period of stable nights and days with well-developed convective boundary layers, a bias of 18 % in the mean daily minimum radon concentration was eliminated by correcting for the instrument response

Estimating the near-surface daily fine aerosol load using hourly Radon-222 observations

We investigate the extent to which hourly radon observations can be used to estimate daily PM2.5 loading near the ground. We formulate, test and apply a model that expresses the mean daily PM2.5 load as a linear combination of observed radon concentrations and differences on a given day. The model was developed using two consecutive years of observations (2007–2008) at four sites near Sydney, Australia, instrumented with aerosol samplers and radon detectors. Model performance was subsequently evaluated against observations in 2009. After successfully reproducing mean daily radon concentrations (r2≥0.98), we used the model to estimate daily PM2.5 mass, as well as that of selected elements (Si, K, Fe, Zn, H, S and Black Carbon). When, parameterizing the model for elemental mass estimates the highest r2 values were generally obtained for H, BC, K and Si. Separating results by season, the r2 values for K and BC were higher in winter for all sites, a period of time where higher concentrations of these elements are seen and a rapid estimation tool would be of particular benefit. The best overall results were obtained in winter for H and BC [r2 = 0.50, 0.68, 0.70, 0.63 (H) and 0.57, 0.57, 0.78, 0.44 (BC)], respectively for Warrawong, Lucas Heights, Richmond and Muswellbrook. Evaluation of model PM2.5 estimates was most successful for days with typical aerosol loads; loads were usually underestimated for, the less frequent, high–to–extreme pollution days. The best elemental results were obtained for BC at Richmond in winter (r2 = 0.68). However, for Warrawong and Lucas Heights r2 values increased from 0.26 to 0.60, and from 0.33 to 0.73, respectively, when several particularly high concentration events were excluded from the analysis. The model performed best at Richmond, an inland site with relatively flat terrain. However, model parameters needto be evaluated for each site. © 2013, Atomospheric Pollution Research (APR)

Vertical radon-222 profiles in the atmospheric boundary layer

Radon-222 (radon) is a naturally occurring radioactive tracer of air mass transport on different time and space scales. In particular, the vertical distribution of radon has been demonstrated to be useful for characterisation of exchange and mixing processes within the atmospheric boundary layer. In 2006 we started a program of research, using radon-222 to advance our understanding of these processes as part of a broader goal to improve parameterisation schemes for vertical mixing in the lower atmosphere. Two types of experiments have been conducted. The first is based on continuous hourly estimates of radon-222 concentration gradients at two meteorological towers, one focussing on near-surface gradients (2-50m) recorded on a 50m tower at Lucas Heights in New South Wales (34.05ºS, 150.98ºE), and the other on boundary layer gradients (20-200 m) measured on a 213m tower at the Cabauw Experimental Site for Atmospheric Research in the Netherlands (51.971ºN, 4.927ºE). The second experiment type relies on the collection of high resolution radon-222 vertical profiles up to 4,000 m above ground level using radon samplers mounted on an instrumented motorised research glider. In this presentation, we discuss selected results from a unique set of high resolution vertical radon profiles measured in 2007-2010 in clear and cloudy daytime terrestrial boundary layers over rural New South Wales. The profile examples reveal the characteristic structure and variability of three major types of daytime boundary layer: 1) dry convective boundary layers, 2) mixed layers topped with residual layers, and 3) convective boundary layers topped with coupled non-precipitating clouds. We demonstrate that important boundary layer processes are identifiable in the observed radon profiles, including ‘‘top down’’ mixing associated with entrainment in clear-sky cases and strongly enhanced venting and sub-cloud layer mixing when substantial active cumulus are present. A related presentation (Chambers et al. 2011) outlines some recent results based on our radon gradient measurements at the Lucas Heights tower. © 2011 CSIRO and the Bureau of Meteorology

Atmospheric mercury in the Southern Hemisphere tropics: Seasonal and diurnal variations and influence of inter-hemispheric transport

Mercury is a toxic element of serious concern for human and environmental health. Understanding its natural cycling in the environment is an important goal towards assessing its impacts and the effectiveness of mitigation strategies. Due to the unique chemical and physical properties of mercury, the atmosphere is the dominant transport pathway for this heavy metal, with the consequence that regions far removed from sources can be impacted. However, there exists a dearth of long-Term monitoring of atmospheric mercury, particularly in the tropics and Southern Hemisphere. This paper presents the first 2 years of gaseous elemental mercury (GEM) measurements taken at the Australian Tropical Atmospheric Research Station (ATARS) in northern Australia, as part of the Global Mercury Observation System (GMOS). Annual mean GEM concentrations determined at ATARS (0.95ĝ€±ĝ€0.12ĝ€ngĝ€mĝ\u273) are consistent with recent observations at other sites in the Southern Hemisphere. Comparison with GEM data from other Australian monitoring sites suggests a concentration gradient that decreases with increasing latitude. Seasonal analysis shows that GEM concentrations at ATARS are significantly lower in the distinct wet monsoon season than in the dry season. T his result provides insight into alterations of natural mercury cycling processes as a result of changes in atmospheric humidity, oceanic/terrestrial fetch, and convective mixing, and invites future investigation using wet mercury deposition measurements. Due to its location relative to the atmospheric equator, ATARS intermittently samples air originating from the Northern Hemisphere, allowing an opportunity to gain greater understanding of inter-hemispheric transport of mercury and other atmospheric species. Diurnal cycles of GEM at ATARS show distinct nocturnal depletion events that are attributed to dry deposition under stable boundary layer conditions. These cycles provide strong further evidence supportive of a qmulti-hop/q model of GEM cycling, characterised by multiple surface depositions and re-emissions, in addition to long-range transport through the atmosphere