ANSTO :: Browsing by Author "Zahorowski, W"

Browsing by Author "Zahorowski, W"

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222Rn calibrated mercury fluxes from terrestrial surfaces of southern Africa derived from observations at Cape Point, South Africa
(EDP Sciences, 2012-09-23) Slemr, F; Brunke, EG; Whittlestone, S; Zahorowski, W; Ebinghaus, R; Kock, HH; Labuschagne, C
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, 2013
222Rn vertical gradient measurements and its use for transport model calibration.
(Energy Research Centre for the Netherlands, 2008-06) Vermeulen, AT; Verheggen, B; Zahorowski, W
222Rn-calibrated mercury fluxes from terrestrial surface of southern Africa
(European Geosciences Union, 2013-01-01) Slemr, F; Brunke, EG; Whittlestone, S; Zahorowski, W; Ebinghaus, R; Kock, HH; Labuschagne, C
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 Union
Application for 222Rn in atmospheric research
(Australian Nuclear Science and Technology Organisation, 2012-10-16) Chambers, SD; Williams, AG; Zahorowski, W; Griffiths, AD
Radon-222 (radon) is a relatively short-lived (half-life 3.82 d), naturally occurring, radioactive gas, with a relatively consistent and well-defined terrestrial flux, and almost negligible oceanic flux. Being a noble, poorly-soluble gas that does not accumulate in the atmosphere, it is an ideal tracer of recent (<2-3 weeks) air mass contact with ice-free terrestrial regions. In conjunction with air mass back trajectory analysis, radon is thus a useful tool with which to perform fetch analyses for observed pollution events. Since radon’s half-life is much greater than the turbulent timescale in the atmospheric boundary layer (~1 hour), it can be considered a conservative tracer in such situations. Consequently, radon profiles or gradient measurements in the lower atmosphere also provide valuable insight into vertical mixing processes under a range of atmospheric conditions. This presentation will provide an overview of ANSTO’s radon measurement capabilities (including: standalone detectors, tall-tower gradient measurements, aircraft profile measurements and flux chambers), with recent examples of their recent application. Radon’s physical characteristics also make it ideal for the evaluation of transport and mixing schemes of weather, climate or chemical models. This presentation will also showcase a radon flux map of Australia, developed at ANSTO to improve the radon source function employed in regional models.
Characterisation of mixing processes in the lower atmosphere using Rn-222 and climate-sensitive gases
(Australian Nuclear Science and Technology Organisation, 2007-08) Schelander, P; Griffiths, AD; Williams, AG; Chambers, SD; Zahorowski, W
Comparison of one- and two-filter detectors for atmospheric 222Rn measurements under various meteorological conditions
(European Geosciences Union, 2010-06-28) Xia, Y; Sartorius, H; Schlosser, C; Stohlker, U; Conen, F; Zahorowski, W
Parallel monitoring of 222Rn and its short-lived progeny (218Po and 214Pb) were carried out from November 2007 to April 2008 close to the top of the Schauinsland mountain, partly covered with forest, in South-West Germany. Samples were aspired from the same location at 2.5 m above ground level. We measured 222Rn with a dual flow loop, two-filter detector and its short-lived progeny with a one-filter detector. A reference sector for events, facing a steep valley and dominated by pasture, was used to minimize differences between 222Rn and progeny-derived 222Rn activity concentrations. In the two major wind sectors covered by forest to a distance between 60 m and 80 m towards the station progeny-derived 222Rn activity concentration was on average equal to 87% (without precipitation) and 74% (with precipitation) of 222Rn activity concentration. The observations show that most of the time both detector types follow the same pattern. Still, there is no single disequilibrium factor that could be used to exactly transform short-lived progeny to 222Rn activity concentration under all meteorological conditions. © Author(s) 2010
Constraining annual and seasonal radon-222 flux density from the Southern Ocean using radon-222 concentrations in the boundary layer at Cape Grim
(Taylor & Francis Group, 2013-02-14) Zahorowski, W; Griffiths, AD; Chambers, SD; Williams, AG; Law, RM; Crawford, J; Werczynski, S
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.
Continuous hourly radon gradient observations at Cabauw, the Netherlands - a review of main features of the 2007-2009 dataset
(Copernicus Publications, 2010-05-02) Zahorowski, W; Vermeulen, AT; Williams, AG; Chambers, SD; Verheggen, B
We report on results of the first three years of radon time series and radon gradient observations at the Cabauw site in the Netherlands (51.971°N, 4.927°E). Two 1500 L dual flow loop, two filter radon detectors with a sensitivity better than 40 mBq m-3 are installed at the site, ensuring that gradients can be defined to the required precision every hour. The inlets are mounted on the main meteorological tower at 20 m and 200 m above ground level. The Cabauw site, located 50 km inland on a polder in an agricultural region, has a simple orography with surface elevations changing by a few metres at most within a 20 km radius. The radon gradient observations are part of our larger program to characterise turbulent mixing processes throughout the lower atmosphere. The two other related measurement projects are the continuous hourly measurements of radon gradients in the surface layer on a 50 m tower at Lucas Heights, Australia (34.053ºS, 150.981ºE; see Chambers et al, this conference), and campaign-style measurements of radon profiles up to altitudes of 4000 m above ground level using light aircraft (see Williams et al., this conference). We observe well pronounced absolute radon and radon gradient signals at Cabauw, influenced by atmospheric processes occurring on seasonal, synoptic, and diurnal time scales. Seasonal variability - the lowest radon concentrations were observed in winter and summer, when the dominant air mass fetch was the Atlantic Ocean. In spring and autumn, concentrations were generally high, as the air mass fetch was primarily over western and/or central Europe. Even when the fetch was oceanic during the latter seasons, it was often over the North Sea where radon concentrations are perturbed by land emissions. In autumn, radon concentrations from the mainland European fetch were more than three times larger than the corresponding concentration from the Atlantic/North Sea regions. Synoptic variability - the radon signal is typically a combination of local and remote influences. Synoptic and diurnal components can be separated by comparing the radon signal at 20 m and 200 m, and by using wind speed as a selecting condition. For most of the data, the diurnal signal is strongly pronounced in the 20 m data, especially when wind speeds are lower than 3 ms-1. In low wind conditions, local influences dominate and the radon signal is predominantly a combination of local source variations and diurnal changes in the local mixing depth. On the other hand, under high wind conditions (> 7 ms-1) the remote signal dominates at both levels, reflecting variations in the radon source function over a wider fetch area, the geographic extent of which is defined by the radon half-life and prevailing wind conditions. The separation of these two signals provides an opportunity to compare subsets of radon time series and gradient observations with a column or regional model and thus evaluate mixing and transport schemes characteristic for the site and the region. Diurnal variability - diurnal composite plots show that the 20 m signal is characterized by an early morning maximum and early afternoon minimum, predominantly reflecting changes in the boundary layer mixing depth on this time scale. The amplitude of this cycle ranged from 450 mBq m-3 in winter to 1460 mBq m-3 in spring. The 200 m Cabauw data exhibited a modest mid-morning maximum, consistent with upward mixing of radon from the surface as the nocturnal inversion breaks down.
Determination of mid-latitude radon-222 flux from the Southern Ocean using atmospheric radon-222 concentration measurements at an island ground station
(International Atomic Energy Agency, 2004-10-24) Zahorowski, W; Chambers, SD; Henderson-Sellers, A
Terrestrial radon (radon-222) fluxes typically exceed oceanic fluxes by 2-3 orders of magnitude [1]. This sometimes leads to the oceanic flux being neglected in atmospheric models [2, 3]. However, direct comparisons between observed and simulated atmospheric radon concentration at remote sites with extended oceanic fetch would benefit from the inclusion of a realistic oceanic radon flux within models [4]. Existing estimates of oceanic radon fluxes are not well constrained, with values ranging over two orders of magnitude (0.0011 - 0.15 atoms cm-2s-1) [1, 5]. At present, the primary factors contributing to the poor characterisation of oceanic radon fluxes are the limited number of observations, and the representativeness of the published results. Previous studies have employed either the accumulation [1] or gradient methods [5]. Both methods are based on spot measurements and as such, are subject to local conditions. More importantly, it would be difficult, if not impossible, to relate such results to a wider range of environmental parameters such as wind speed and sea state, which have a significant effect on ocean-atmosphere exchange. We present a method for the determination of regional oceanic radon fluxes. The method is applied to a subset of high sensitivity hourly atmospheric radon concentration observations from 1999 to 2003 made at Cape Grim, Tasmania (40°41’S, 144°41’E), a World Meteorological Organisation Global Atmosphere Watch (WMO GAW) station. A simple expression for an average oceanic radon flux is derived and applied using a subset of the observations considered to be representative of air parcels with an extended oceanic fetch. We discuss the dataset using the notion of an ‘oceanic event’, which is defined here as any set of consecutive hourly observations coming from the oceanic sector. Typically, the duration of a single oceanic event will vary from a few hours to a few days. The intermittent nature of boundary layer wind fields can result in short-term transitions across the oceanic sector boundaries when the air mass has mixed origins. Since the terrestrial radon source is much stronger than the oceanic source, only oceanic events that persist on synoptic time-scales are likely to include hourly observations that are representative of a minimally perturbed oceanic fetch. The evolution of radon concentration in the composite oceanic event was examined. It was found that radon concentrations in the first 20-30 hours after change to the oceanic sector are strongly perturbed from oceanic values. After the initial 20-30 hours, mean radon concentrations in the composite oceanic event are within the 95% confidence interval. This suggests that radon concentrations from this portion of the composite oceanic event are minimally perturbed from typical oceanic values. The lowest value in the range of estimated mean radon flux from the region of the Southern Ocean within the Cape Grim radon measurement fetch is about 0.0026 atoms cm-2s-1. This value is thought to constitute a lower limit estimate since it was obtained assuming negligible loss of radon from the marine boundary layer to the free troposphere. Taking into account the entrainment of radon from the marine boundary layer to the lowest layer within the free troposphere, derived from airborne measurements of mixing of dimethyl sulphide and aerosol particles over the Southern Ocean, leads to an upper limit estimate of about 0.006 atoms cm- 2s-1. Based on the 10 and 90 percentile radon concentration and wind speed observations, and assuming a mechanically driven mixing height, the regional oceanic radon flux may vary from 0.0014 to 0.008 atoms cm-2s-1 with changes in the sea state induced by wind and other environmental parameters. Our findings support the common assumption that oceanic radon fluxes are 2-3 orders of magnitude lower than terrestrial radon fluxes, which are typically within the range 0.5-2 atoms cm-2s-1. Our values are lower than some experimental spot estimates of oceanic radon flux rates made in the seventies [1, 5]. However, they are in close agreement with more recent estimates of the flux derived from model evaluation studies and also with radon flux values assumed in an intercomparison of the convective and synoptic processes of 20 global atmospheric transport models sponsored by the World Climate Research Program [4]. The new method of oceanic radon flux derivation can be applied to other sites around the world where ‘clean’ ocean air can be clearly identified. The method offers an alternative to experimental local/spot estimates of oceanic radon flux such as the accumulation method and gradient methods. More importantly, it is representative of a large region and allows results to be related to a wider range of environmental parameters that influence sea state (e.g. wind speed), which have a significant effect on ocean-atmosphere exchange.
Estimating the Asian radon flux density and its latitudinal gradient in winter using ground-based radon observations at Sado Island
(Wiley-Blackwell, 2009-11) Williams, AG; Chambers, SD; Zahorowski, W; Crawford, J; Matsumoto, K; Uematsu, M
Terrestrial radon-222 flux density for the Asian continent, integrated over distances of 4500 km, is estimated in two 20° latitudinal bands centred on 48.8°N and 63.2°N. The evaluation is based on three years of wintertime radon measurements at Sado Island, Japan, together with meteorological and trajectory information. A selection of 18% of observations are suitable for evaluation of an analytical expression for the continental surface flux. Various meteorological assumptions are discussed; it is found that there is a substantial effect of increased complexity of the formulation on the flux estimates obtained. The distribution of spatially integrated radon flux over the Asian landmass is reported for the first time. Expressed as geometric means and 1σ-ranges, estimated fluxes are 14.1 mBq m−2 s−1 (1σ-range: 18 mBq m−2 s−1) and 8.4 mBq m−2 s−1 (1σ-range: 10 mBq m−2 s−1) for the lower and higher latitude bands. These results constitute an annual minimum in flux densities for these regions, and are higher than previously reported. The existence of a latitudinal gradient in the continental radon source function is confirmed; the present estimate for Asia (−0.39 mBq m−2 s−1 per degree of latitude) is in agreement with the northern hemisphere terrestrial radon flux gradient proposed previously. © 2009, Wiley-Blackwell.
Estimating the near-surface daily fine aerosol load using hourly Radon-222 observations
(Atmospheric Pollution Research (APR), 2013-01-01) Crawford, J; Zahorowski, W; Cohen, DD; Chambers, SD; Stelcer, E; Werczynski, S
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).
Estimation of the molecular hydrogen soil uptake and traffic emissions at a suburban site near Paris through hydrogen, carbon monoxide, and radon-222 semicontinuous measurements.
(American Geophysical Union, 2009-09-23) Yver, C; Schmidt, M; Bousquet, P; Zahorowski, W; Ramonet, M
Since June 2006, simultaneous semicontinuous measurements of tropospheric molecular hydrogen (H2), carbon monoxide (CO), and radon-222 (222Rn) have been performed at Gif-sur-Yvette (Paris region), a suburban atmospheric measurement site in France. Molecular hydrogen mixing ratios range from 500 to 1000 ppb, CO mixing ratios vary from 100 to 1400 ppb, and 222Rn concentrations fluctuate from 0 to 20 Bq m−3. The H2 seasonal cycle shows the expected pattern for the Northern Hemisphere with a maximum in spring and a minimum in autumn. We inferred a mean baseline value of 533 ppb with a peak-to-peak amplitude of 30 ppb. Carbon monoxide exhibits a seasonal cycle with a maximum in winter and a minimum in summer. The mean baseline value reaches 132 ppb with a peak-to-peak amplitude of 40 ppb. Radon-222 presents weak seasonal variations with a maximum in autumn/winter and a minimum in spring/summer. The diurnal cycles of H2 and CO are dominated by emissions from nearby traffic with two peaks during morning and evening rush hours. The typical H2/CO emission ratio from traffic is found to be 0.47 ± 0.08 on a molar basis (ppb/ppb). The radon tracer method is applied to nighttime H2 observations to estimate the H2 soil uptake of the nocturnal catchment area of our sampling site. The influences from nocturnal local anthropogenic combustion sources are estimated by parallel measurements of CO at 0.14 × 10−5 g(H2) m−2 h−1. The mean inferred dry deposition velocity is 0.024 ± 0.013 cm s−1 with a seasonal amplitude of 40% at Gif-sur-Yvette. © 2009, American Geophysical Union
Evaluating radon-derived mixing depth as a potential length scale for nocturnal mixing processes over land.
(European Geosciences Union, 2010-05-02) Chambers, SD; Williams, AG; Zahorowski, W; Griffiths, AD
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.
Evidence for nearly complete decoupling of very stable nocturnal boundary layer overland
(Springer, 2011-01-01) Xia, Y; Conen, F; Haszpra, L; Ferenczi, Z; Zahorowski, W
Concentrations of (222)Rn at 0.1 m and 6.5 m height above ground level and (222)Rn flux density were measured during nights characterized by strong cooling, light winds and clear sky conditions in the Carpathian Basin in Hungary. A very stable boundary layer (vSBL) formed on 14 nights between 15 August and 3 September 2009. On 12 nights, an estimated 72% (s.d. 20%) of (222)Rn emitted from the surface since sunset was retained within the lowest 6.5 m above the ground until sunrise the following morning. On two nights an intermittent increase in wind speed at 9.4 m height was followed by a rise in temperature at 2.0 m height, indicating a larger atmospheric motion that resulted in (222)Rn at 0.1 m around sunrise being the same as around the preceding sunset. It does not seem to be rare in a large continental basin for a vSBL to be nearly completely decoupled from the atmosphere above for the entire period from sunset to sunrise. © 2011, Springer.
A global transport model comparison for methane: results for two Australian sites
(International Union of Geodesy and Geophysics, 2011-07-06) Law, RM; Loh, ZM; Corbin, KD; Krummel, PB; Steele, LP; Fraser, PJ; Etheridge, DM; Zahorowski, W
Methane (CH4) is an important greenhouse gas. Using atmospheric CH4 measurements to estimate CH4 emissions requires a good understanding of how CH4 is transported in the atmosphere. Hence, simulations of atmospheric CH4 concentration have been made with two atmospheric models, namely ACCESS and CCAM, as part of the Transport Model Intercomparison project, TransCom-CH4. The simulations ran for the period 1990-2008 and used six different sets of surface CH4 emissions, while the chemical CH4 sink was modelled using prescribed OH and stratospheric loss fields. Radon, sulphur hexafluoride and methyl chloroform tracers were also simulated. Model output has been analysed for two Australian sites with in-situ CH4 measurements: Cape Grim, Tasmania (AGAGE in-situ data) and the CO2CRC Otway project, Victoria. Cape Grim is a coastal site, observing periods of clean (baseline) air from the Southern Ocean and periods of non-baseline air, influenced by emissions from South Eastern Australia including Melbourne. Otway is a rural location, 4 km from the coast, where the land use is predominantly dairy farming, resulting in a large local CH4 signal from enteric fermentation (diurnal amplitudes up to 250 ppb). Nevertheless, during well mixed periods, measured CH4 concentrations at Otway may be similar to the baseline CH4 concentrations measured at Cape Grim or represent broader regional South Eastern Australian emissions. Preliminary findings indicate that CH4 at Otway and non-baseline CH4 at Cape Grim are sensitive to the choice of wetland emissions. There is also some indication that Melbourne emissions may be underestimated in these simulations.
H(2) Vertical profiles in the continental boundary layer: measurements at the Cabauw tall tower in the Netherlands
(Copernicus Gesellschaft MBH, 2011-07-01) Popa, ME; Vermeulen, AT; van den Bulk, WCM; Jongejan, PAC; Batenburg, AM; Zahorowski, W; Röckmann, T
In-situ, quasi-continuous measurements of atmospheric hydrogen (H(2)) have been performed since October 2007 at the Cabauw tall tower station in the Netherlands. Mole fractions of H(2), CO and several greenhouse gases are determined simultaneously in air sampled successively at four heights, between 20 and 200 m above ground level. (222)Rn measurements are performed in air sampled at 20 and 200 m. This H(2) dataset represents the first in-situ, quasi-continuous long-term measurement series of vertical profiles of H(2) in the lower continental boundary layer. Seasonal cycles are present at all heights in both H(2) and CO, and their amplitude varies with the sampling height. The seasonality is evident in both the "baseline" values and in the short term (diurnal to synoptic time scales) variability, the latter being significantly larger during winter. The observed H(2) short term signals and vertical gradients are in many cases well correlated to other species, especially to CO. On the other hand, H(2) has at times a unique behaviour, due to its particular distribution of sources and sinks. Our estimation for the regional H(2) soil uptake flux, using the radon tracer method, is (-1.89 +/- 0.26) x10(-5) g/(m(2) h), significantly smaller than other recent results from Europe. H(2)/CO ratios of the traffic emissions computed from our data, with an average of 0.54 +/- 0.07 mol: mol, are larger and more variable than estimated in some of the previous studies in Europe. This difference can be explained by a different driving regime, due to the frequent traffic jams in the influence area of Cabauw. The H(2)/CO ratios of the large scale pollution events have an average of 0.36 +/- 0.05 mol:mol; these ratios were observed to slightly increase with sampling height, possibly due to a stronger influence of soil uptake at the lower sampling heights. © Author(s) 2011.
High sensitivity two filter radon/thoron detectors with a wire or nylon screen as a second filter.
(Australian Nuclear Science and Technology Organisation, 1994-12) Whittlestone, S; Zahorowski, W; Wasiolek, P
A study is made of the use of wire and nylon screens as a second filter in two radon or thoron detectors. It is shown that acceptable detection efficiency is obtained at flow rates comparable to those used in detectors in which other types of filter are used. The main advantage of the screens is their very low flow impedance. Several designs of detector which exploit this feature are discussed. Details are given of the performance of three prototypes: a 32 L radon detector with a limit of detection of 0.0027 Bq m-3 and power consumption of 25 watts; and a portable thoron emanometer capable of detecting fluxes as low as 1 m Bq m -2 s-1. The radon detectors are rugged and simple. They can operate with no routine maintenance and are suited to remote locations where only infrequent technical support is available.
Human activity and climate variability project: annual report 2001.
(Australian Nuclear Science and Technology Organisation, 2002-01) Harle, KJ; Heijnis, H; Henderson-Sellers, A; Sharmeen, S; Zahorowski, W
Knowledge of the state of the Australian environment including natural climate variability prior to colonial settlement is vital if we are to define and understand the impact of over two hundred years of post-industrial human activity on our landscape. ANSTO in conjunction with university partners is leading a major research effort to provide natural archives of human activity and climate variability over the last 500 years in Australia utilising a variety of techniques including lead-210 and radiocarbon dating and analyses of proxy indicators (such as microfossils) as well as direct evidence (such as trace elements) of human activity and climate variability. The other major project objectives were to contribute to the understanding of the impact of human induced and natural aerosols in the East Asian region on climate through analysis and sourcing of fine particles and characterisation of air samples using radon concentrations and to contribute to the improvement of land surface parameterisation schemes and investigate the potential to use stable isotopes to improve global climate models and thus improve our understanding of future climate.
Human activity and climate variability project: annual report 2002.
(Australian Nuclear Science and Technology Organisation, 2002-11) Chambers, SD; Harle, KJ; Sharmeen, S; Zahorowski, W; Cohen, DD; Heijnis, H; Henderson-Sellers, A
This project aims to utilise nuclear techniques to investigate evidence of human activity and climate variability in the Asia Australasian regions. It was originally designed to run over three years, commencing July 1999, with three parallel research tasks: Task 1: Past -- Natural archives of human activity and climate variability; Task 2: Present -- Characterisation of the global atmosphere using radon and fine particles; Task 3: Future -- Climate modelling: evaluation and improvement; Main project objectives -- To determine what proportions of changes in natural archives are due to human activity and climate variability; -- To contribute to the understanding of the impact of human induced and natural aerosols in the East Asian region on climate through analysis and sourcing of fine particles and characterisation of air samples using radon concentrations; -- To contribute to the improvement of land surface parameterisation schemes and investigate the potential to use isotopes to improve global climate models and thus improve our understanding of future climate. Significant project outcomes -- An improved understanding of natural and anthropogenic factors influencing change in our environment; -- A better understanding of the role of aerosols in climate forcing in the Asian region, leading to improved ability to predict climate change; -- An improved understanding of long term changes in the concentrations of trace species in the atmosphere on a regional and a global basis and their use in model evaluation; -- Improved understanding of the impact of different land-surface schemes on simulations by atmospheric models. The next two years of the project Our new and extended projects efforts include: 1) Aligning ourselves with the recently developed mission of the IGBP/PAGES research program 'Human Interactions on Terrestrial Ecosystems' and co-ordinating the Australasian research effort. Further research will focus on: (1) How widespread and reliable are evidence of major climatic events, such as storms and El Nino/La Nina cycles, in natural archives? This would require more natural archives to be examined from northern Australia and also records to be obtained from southern Australia. (2) The spatial extent of mining related pollutants, in the form of aerosol particles, which is of importance to managing the waste in the future. A combination of aerosol and archival studies will address this issue. In Summary: To achieve these extended goals we successfully gained another two years of further support for our project.
Identifying tropospheric baseline air masses at mauna loa observatory between 2004 and 2010 using radon-222 and back trajectories
(John Wiley and Sons, 2013-01-16) Chambers, SD; Zahorowski, W; Williams, AG; Crawford, J; Griffiths, AD
We use 7 years of hourly radon observations at Mauna Loa Observatory (MLO), together with 10-day back trajectories, to identify baseline air masses at the station. The amplitude of the annual MLO radon cycle, based on monthly means, was 98 mBq m–3 (39 –137 mBq m–3), with maximum values in February (90th percentile 330 mBq m–3) and minimum values in August (10th percentile 8.1 mBq m–3). The composite diurnal radon cycle (amplitude 49 mBq m–3) is discussed with reference to the influences of local flow features affecting the site, and a 3-hour diurnal sampling window (0730–1030 HST) is proposed for observing the least terrestrially influenced tropospheric air masses. A set of 763 baseline events is selected, using the proposed sampling window together with trajectory information, and presented along with measured radon concentrations as a supplement. This data set represents a resource for the selection of baseline events at MLO for use with a range of trace species. A reduced set of 196 “deep baseline” events occurring in the July–September window is also presented and discussed. The distribution (10th/50th/90th percentile) of radon in deep-baseline events (8.7/29.2/66.1 mBq m–3) was considerably lower than that for the overall set of 763 baseline events (12.3/40.8/104.1 mBq m–3). Results from a simple budget calculation, using sonde-derived mixing depths and literature-based estimates of oceanic radon flux and radon concentrations in the marine boundary layer, indicate that the main source of residual radon in the lower troposphere under baseline conditions at MLO is downward mixing from aged terrestrial air masses in the upper troposphere. © 2012, American Geophysical Union.

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