On the use of radon for quantifying the effects of atmospheric stability on urban emissions

Radon is increasingly being used as a tool for quantifying stability influences on urban pollutant concentrations. Bulk radon gradients are ideal for this purpose, since the vertical differencing substantially removes contributions from processes on timescales greater than diurnal and (assuming a constant radon source) gradients are directly related to the intensity of nocturnal mixing. More commonly, however, radon measurements are available only at a single height. In this study we argue that single-height radon observations should not be used quantitatively as an indicator of atmospheric stability without prior conditioning of the time series to remove contributions from larger-scale "non-local" processes. We outline a simple technique to obtain an approximation of the diurnal radon gradient signal from a single-height measurement time series, and use it to derive a four category classification scheme for atmospheric stability on a "whole night" basis. A selection of climatological and pollution observations in the Sydney region are then subdivided according to the radon-based scheme on an annual and seasonal basis. We compare the radon-based scheme against a commonly used Pasquill–Gifford (P–G) type stability classification and reveal that the most stable category in the P–G scheme is less selective of the strongly stable nights than the radon-based scheme; this lead to significant underestimation of pollutant concentrations on the most stable nights by the P–G scheme. Lastly, we applied the radon-based classification scheme to mixing height estimates calculated from the diurnal radon accumulation time series, which provided insight to the range of nocturnal mixing depths expected at the site for each of the stability classes. © 2015, Author(s)

Characterising terrestrial influences on Antarctic air masses using Radon-222 measurements at King George Island

We report on one year of high-precision direct hourly radon observations at King Sejong Station (King George Island) beginning in February 2013. Findings are compared with historic and ongoing radon measurements from other Antarctic sites. Monthly median concentrations reduced from 72 mBq m−3 in late-summer to 44 mBq m−3 in late winter and early spring. Monthly 10th percentiles, ranging from 29 to 49 mBq m−3, were typical of oceanic baseline values. Diurnal cycles were rarely evident and local influences were minor, consistent with regional radon flux estimates one tenth of the global average for ice-free land. The predominant fetch region for terrestrially influenced air masses was South America (47–53° S), with minor influences also attributed to aged Australian air masses and local sources. Plume dilution factors of 2.8–4.0 were estimated for the most terrestrially influenced (South American) air masses, and a seasonal cycle in terrestrial influence on tropospheric air descending at the pole was identified and characterised. © Author(s) 201

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

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

Improving the Representation of Cross-Boundary Transport of Anthropogenic Pollution in East Asia Using Radon-222.

We report on 10 years of hourly atmospheric radon, CO, and SO2 observations at Gosan Station, Korea. An improved radon detector was installed during this period and performance of the detectors is compared. A technique is developed whereby the distribution of radon concentrations from a fetch region can be used to select air masses that have consistently been in direct contact with land-based emissions, and have been least diluted en route to the measurement site. Hourly radon concentrations are used to demonstrate and characterise contamination of remote-fetch pollution observations by local emissions at this key WMO GAW site, and a seasonally-varying 5-hour diurnal sampling window is proposed for days on which diurnal cycles are evident to minimise these effects. The seasonal variability in mixing depth and “background” pollutant concentrations are characterised. Based on a subset of observations most representative of the important regional fetch areas for this site, and least affected by local emissions, seasonal estimates of CO and SO2 in air masses originating from South China, North China, Korea and Japan are compared across the decade of observations. 2016, © Taiwan Association for Aerosol Researc

Seasonal variability of the radon-222 flux density from the Southern Ocean derived from atmospheric radon-222 measurements at the Cape Grim baseline station in Tasmania.

We present and discuss an estimate of the radon-222 (radon) flux density from the Southern Ocean and its seasonal variability. The flux estimate was based on selected hourly atmospheric radon concentration measurements in the Baseline wind sector of the Cape Grim station in Tasmania (40°41’S, 144°41’22”E) from 2001 to 2008. The aim of the selection process was to define a subset of hourly radon observations corresponding to oceanic air parcels that were least perturbed by land emissions and exhibiting minimal exchange with the free troposphere, so that an equilibrium could be assumed between the measured radon concentrations and their oceanic source. The initial dataset included all events in the Cape Grim Baseline sector, defined solely by local wind direction (190º< Ө <280º). In this set, more than 75% of the hourly radon observations were already below 100 mBq m-3. We demonstrate that the strongest perturbation due to land emissions occurs at the beginning and end of each baseline period, with the duration of these transitional periods being 24 and 12 hours, respectively. Additional statistically significant terrestrial radon emissions and near-shore influences were identified and quantified by analysing special features of 10-day back trajectories, calculated using the HYSPLIT model, and the associated radon distributions. We show that the Australian terrestrial influence leads to an upward shift of the corresponding radon distributions, with the converse being true for Antarctic terrestrial influence. Statistically significant near-shore influences were attributed to horizontal radon gradients extending from the coast over the ocean, south from the Australian mainland and north from the Antarctic sea ice boundary. Progressive application of the selection criteria contracts radon distributions of the resulting subsets, with the higher percentile concentrations undergoing the most pronounced reductions. For example, the concentration ranges of 90% of baseline observations (ie. from the 5th to 95th percentiles) were 483, 165, 126, 90, and 88 mBq m-3 for the five major radon sub-sets considered with progressively stringent selection criteria. The progressive reduction in concentration range for each category confirms the efficacy of the selections made, since the narrower the concentration range, the more homogenous the radon source probed by the observations. We also found that the more that the terrestrial influences could be reduced, the more clearly revealed was the seasonal variability in flux estimates. The ratio of summer to winter median radon concentrations increases from 1.13 for all baseline observations, to 1.6 for the final subset of baseline observations (considered to include only those radon observations corresponding to air parcels most closely in equilibrium with their oceanic radon source). The final dataset included 900 hourly radon observations, about 3% of all baseline events recorded in the 2001-2008 period. The marine boundary layer heights required for the flux estimates were derived from an ECMWF operational model reanalysis on a 1.5° grid. We compared the reanalysis for 1998 with mini-lidar measurements gathered at Cape Grim and found that on average the lidar estimates were approximately 11% lower. Assuming that the application of our stringent selection criteria also excluded meteorological events such as frontal passage and significant boundary layer venting by deep active cumulus, we employed an entrainment velocity typical of the Southern Ocean marine boundary layer in the study region (0.004 ms-1 ±0.002 ms-1). The flux density means calculated using the above assumptions, expressed in units of mBq m-2s-1 were 0.27 ±0.10, 0.30 ±0.11, and 0.19 ±0.07 for the 2001-2008 composite year, winter, and summer, respectively, with the stated uncertainties resulting from uncertainties in the estimates of marine boundary layer heights at Cape Grim, and of the assumed entrainment velocity.European Geosciences Unio

Numerical simulation of barge impact on a continuous girder bridge and bridge damage detection

Vessel collisions on bridge piers have been frequently reported. As many bridges are vital in transportation networks and serve as lifelines, bridge damage might leads to catastrophic consequences to life and economy. Therefore it is of great importance to protect bridge structures, especially bridge piers, against vessel impacts. Many researches have been conducted to predict vessel impact loads on bridge piers, and to design bridge piers or additional protective structures to resist such impact loads. Studies on assessing the bridge conditions after a vessel impact are, however, very limited. Current practice basically uses visual inspections, which not only requires very experienced engineers to perform the inspection in order to obtain creditable assessment, but also is often very difficult to inspect the underwater pier conditions. Therefore it is necessary to develop methods to give efficient, quantitative and reliable assessment of bridge conditions under ambient conditions after a vessel impact. This study explores the feasibility of using vibration measurements to quickly detect bridge conditions after a vessel impact.The study consists of three parts. First, a detailed numerical model of an example bridge structure is developed to calculate the vibrations under ambient hydrodynamic force. Then the model is used to simulate vessel impact on bridge pier and predict the pier damage. The vibration response analysis of the damaged bridge model is performed again in the third step to simulate vibration responses of the damaged bridge under ambient conditions. Using the vibration data obtained before and after vessel impact, the bridge vibration parameters such as vibration frequencies and mode shapes are extracted by using the frequency domain decomposition method. The bridge condition will then be identified through the changes in bridge vibration parameters and compared with the damage observed in the impact simulation. It is found that this method is capable of estimating bridge damage condition after barge impact accident

Exoanal ultrasound of the anal sphincter: normal anatomy and sphincter defects

To describe the sonographic appearance of normal anal sphincter anatomy and sphincter defects evaluated with a conventional 5 MHz convex transducer placed on the perineum. Design Prospective, single-blind study. Setting Department of Obstetrics and Gynecology, University of Michigan Medical Center, USA. Population Twenty-five women with symptoms of faecal incontinence, 11 asymptomatic nulliparous women, and 32 asymptomatic parous women. Methods A convex scanner was placed on the perineum with the woman in lithotomy position. Images were taken at three levels of the sphincter canal. Pictures were evaluated by two examiners who were blinded to the case history of the women and to the results of each other for the presence or absence of sphincter defects. Main outcome measures Description of anal sphincter appearance on endoanal ultrasound. Reproducibilty of the evaluation of sphincter defects. Results The internal anal sphincter is visible as a hypoechoic circle; the external anal sphincter shows a hyperechoic pattern. Proximally the sling of the puborectalis muscle is visible. Sphincter defects were detected in 20 women. In all five women who subsequently underwent surgery, the presence and location of the defect was confirmed at the time of surgery. Examiners were in agreement 100% of the time on the presence or absence of internal defects. They disagreed in one patient on the presence of an external defect. Conclusion Exoanal ultrasound provides information on normal anatomy and on defects of the anal sphincter.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75125/1/j.1471-0528.1997.tb12056.x.pd

Translation invariant extensions of finite volume measures

We investigate the following questions: Given a measure μΛ on configurations on a subset Λ of a lattice L, where a configuration is an element of ΩΛ for some fixed set Ω, does there exist a measure μ on configurations on all of L, invariant under some specified symme- try group of L, such that μΛ is its marginal on configurations on Λ? When the answer is yes, what are the properties, e.g., the entropies, of such measures? Our primary focus is the case in which L = Zd and the symmetries are the translations. For the case in which Λ is an interval in Z we give a simple necessary and sufficient condition, local translation invariance (LTI), for extendibility. For LTI measures we construct extensions having maximal entropy, which we show are Gibbs measures; this construction extends to the case in which L is the Bethe lattice. On Z we also consider extensions supported on periodic configurations, which are analyzed using de Bruijn graphs and which include the extensions with minimal entropy. When Λ ⊂ Z is not an interval, or when Λ ⊂ Zd with d > 1, the LTI condition is necessary but not sufficient for extendibility. For Zd with d > 1, extendibility is in some sense undecidable

Primordial Black Holes: sirens of the early Universe

Primordial Black Holes (PBHs) are, typically light, black holes which can form in the early Universe. There are a number of formation mechanisms, including the collapse of large density perturbations, cosmic string loops and bubble collisions. The number of PBHs formed is tightly constrained by the consequences of their evaporation and their lensing and dynamical effects. Therefore PBHs are a powerful probe of the physics of the early Universe, in particular models of inflation. They are also a potential cold dark matter candidate.Comment: 21 pages. To be published in "Quantum Aspects of Black Holes", ed. X. Calmet (Springer, 2014