One year of 222 Rn concentration in the atmospheric surface layer
TL;DR: In this article, a one-year time series of radon measured in a rural area in the North of Italy in 1997 has been analyzed, where wavelet analysis is used as one of the investigation tools of the time series.
Abstract: A one-year time series of 222 Rn measured in a rural area in the North of Italy in 1997 is analyzed. The scope of the investigation is to better understand the behavior of this common atmospheric tracer in relation to the meteorological conditions at the release site. Wavelet analysis is used as one of the investigation tools of the time series. The measurements and scalograms of 222 Rn are compared to those of wind-speed, pressure, relative humidity, temperature and NO x . The use of wavelet analysis allows the identification of the various scales controlling the influence of the meteorological variables on 222 Rn dispersion in the surface layer that are not visible through classical Fourier analysis or direct time series inspection. The analysis of the time series has identified specific periods during which the usual diurnal variation of radon is superimposed to a linear growth thus indicating the build up of concentration at the measurement level. From these specific cases an estimate of the surface flux of 222 Rn is made. By means of a simple model these special cases are reproduced.
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TL;DR: In this paper, the authors synthesize the published literature on subsurface airflow driven by natural forcings such as atmospheric pressure fluctuations, topographic effect, water table fluctuations, and water infiltration.
Abstract: [1] Subsurface airflow in unsaturated zones induced by natural forcings is of importance in many environmental and engineering fields, such as environmental remediation, water infiltration and groundwater recharge, coastal soil aeration, mine and tunnel ventilation, and gas exchange between soil and atmosphere. This review synthesizes the published literature on subsurface airflow driven by natural forcings such as atmospheric pressure fluctuations, topographic effect, water table fluctuations, and water infiltration. The present state of knowledge concerning the mechanisms, analytical and numerical models, and environmental and engineering applications related to the naturally occurring airflow is discussed. Airflow induced by atmospheric pressure fluctuations is studied the most because of the applications to environmental remediation and transport of trace gases from soil to atmosphere, which are very important in understanding biogeochemical cycling and global change. Airflow induced by infiltration is also an extensively investigated topic because of its implications in rainfall infiltration and groundwater recharge. Airflow induced by water table fluctuations is important in coastal areas because it plays an important role in coastal environmental remediation and ecological systems. Airflow induced by topographic effect is studied the least. However, it has important applications in unsaturated zone gas transport and natural ventilation of mines and tunnels. Finally, the similarities and differences in the characteristics of the air pressure and airflow are compared and future research efforts are recommended.
73 citations
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TL;DR: In this article, the authors 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.
Abstract: . 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.
63 citations
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TL;DR: The seasonality of indoor Rn concentration measured in Austria is investigated as a function of other factors that influence indoors Rn, with higher Rn levels in winter.
Abstract: In general, indoor radon concentration is subject to seasonal variability. The reasons are to be found (1) in meteorological influence on the transport properties of soil, e.g. through temperature, frozen soil layers and soil water saturation; and (2) in living habits, e.g. the tendency to open windows in summer and keep them closed in winter, which in general leads to higher accumulation of geogenic Rn in closed rooms in winter. If one wants to standardize indoor Rn measurements originally performed at different times of the year, e.g. in order to make them comparable, some correction transform as a function of measurement time which accounts for these effects must be estimated. In this paper, the seasonality of indoor Rn concentration measured in Austria is investigated as a function of other factors that influence indoor Rn. Indoor radon concentration is clearly shown to have seasonal variability, with higher Rn levels in winter. However, it is complicated to quantify the effect because, as a consequence of the history of an Rn survey, the measurement season maybe correlated to geological regions, which may introduce a bias in the estimate of the seasonality amplitude.
58 citations
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TL;DR: In this paper, a technique recently developed for stability classification using a research-quality dual-flow-loop two-filter radon detector is adapted for use with a commercially available radon-based stability monitor.
Abstract: Commercially-available “stability monitors” based on in situ atmospheric radon progeny measurements remain underutilised as a tool for urban pollution studies, due in part to difficulties experienced in relating their standard output directly to the atmospheric mixing state in a consistent manner. The main confounding factor has been a lack of attention to the fact that the observed near-surface atmospheric radon concentration includes large synoptic and fetch-related components in addition to the local stability influence. Here, a technique recently developed for stability classification using a research-quality dual-flow-loop two-filter radon detector is adapted for use with a commercially-available radon-based stability monitor. Performance of the classification scheme is then tested in Lanzhou, China, a topographically-complex region renowned for low mean annual wind speeds (0.8 m s −1 ) and winter stagnation episodes. Based on an 11-month composite, a factor of seven difference is estimated between peak NO x concentrations in the city's industrial region and a rural background location under stable conditions. The radon-based scheme is evaluated against the Pasquil-Gifford “radiation” (PGR) scheme, and assigns pollutant concentrations more consistently between defined atmospheric stability states than the PGR scheme. Furthermore, the PGR scheme consistently underestimates all peak pollutant concentrations under stable conditions compared with the radon-based scheme, in some cases (e.g. CO in the industrial region) by 25%.
45 citations
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TL;DR: In this article, the authors quantify the land-surface influence at Jungfraujoch hour by hour and detect the presence of anabatic winds on a daily basis during 2010-2011, but only from April to September.
Abstract: . Atmospheric composition measurements at Jungfraujoch are affected intermittently by boundary-layer air which is brought to the station by processes including thermally driven (anabatic) mountain winds. Using observations of radon-222, and a new objective analysis method, we quantify the land-surface influence at Jungfraujoch hour by hour and detect the presence of anabatic winds on a daily basis. During 2010–2011, anabatic winds occurred on 40% of days, but only from April to September. Anabatic wind days were associated with warmer air temperatures over a large fraction of Europe and with a shift in air-mass properties, even when comparing days with a similar mean radon concentration. Excluding days with anabatic winds, however, did not lead to a better definition of the unperturbed aerosol background than a definition based on radon alone. This implies that a radon threshold reliably excludes local influences from both anabatic and non-anabatic vertical-transport processes.
38 citations
References
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TL;DR: In this article, a step-by-step guide to wavelet analysis is given, with examples taken from time series of the El Nino-Southern Oscillation (ENSO).
Abstract: A practical step-by-step guide to wavelet analysis is given, with examples taken from time series of the El Nino–Southern Oscillation (ENSO). The guide includes a comparison to the windowed Fourier transform, the choice of an appropriate wavelet basis function, edge effects due to finite-length time series, and the relationship between wavelet scale and Fourier frequency. New statistical significance tests for wavelet power spectra are developed by deriving theoretical wavelet spectra for white and red noise processes and using these to establish significance levels and confidence intervals. It is shown that smoothing in time or scale can be used to increase the confidence of the wavelet spectrum. Empirical formulas are given for the effect of smoothing on significance levels and confidence intervals. Extensions to wavelet analysis such as filtering, the power Hovmoller, cross-wavelet spectra, and coherence are described. The statistical significance tests are used to give a quantitative measure of change...
11,219 citations
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TL;DR: Wavelet transforms are recent mathematical techniques, based on group theory and square integrable representations, which allows one to unfold a signal, or a field, into both space and scale, and possibly directions.
Abstract: Wavelet transforms are recent mathematical techniques, based on group theory and square integrable representations, which allows one to unfold a signal, or a field, into both space and scale, and possibly directions. They use analyzing functions, called wavelets, which are localized in space. The scale decomposition is obtained by dilating or contracting the chosen analyzing wavelet before convolving it with the signal. The limited spatial support of wavelets is important because then the behavior of the signal at infinity does not play any role. Therefore the wavelet analysis or syn thesis can be performed locally on the signal, as opposed to the Fourier transform which is inherently nonlocal due to the space-filling nature of the trigonometric functions. Wavelet transforms have been applied mostly to signal processing, image coding, and numerical analysis, and they are still evolving. So far there are only two complete presentations of this topic, both written in French, one for engineers (Gasquet & Witomski 1 990) and the other for mathematicians (Meyer 1 990a), and two conference proceedings, the first in English (Combes et al 1 989), the second in French (Lemarie 1 990a). In preparation are a textbook (Holschneider 199 1 ), a course (Dau bee hies 1 99 1), three conference procecdings (Mcyer & Paul 199 1 , Beylkin et al 199 1b, Farge et al 1 99 1), and a special issue of IEEE Transactions
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398 citations
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Harvard University1, University of California, Irvine2, National Center for Atmospheric Research3, York University4, Lawrence Livermore National Laboratory5, Langley Research Center6, University of Washington7, University of Cambridge8, Max Planck Society9, Centre national de la recherche scientifique10, Georgia Institute of Technology11, German Aerospace Center12, University at Albany, SUNY13, University of East Anglia14, Royal Netherlands Meteorological Institute15
TL;DR: In this article, simulations of 222Rn and other short-lived tracers are used to evaluate and intercompare the representations of convective and synoptic processes in 20 global atmospheric transport models.
Abstract: Simulations of 222Rn and other short-lived tracers are used to evaluate and intercompare the representations of convective and synoptic processes in 20 global atmospheric transport models. Results show that most established three-dimensional models simulate vertical mixing in the troposphere to within the constraints offered by the observed mean 222Rn concentrations and that subgrid parameterization of convection is essential for this purpose. However, none of the models captures the observed variability of 222Rn concentrations in the upper troposphere, and none reproduces the high 222Rn concentrations measured at 200 hPa over Hawaii. The established three-dimensional models reproduce the frequency and magnitude of high-222Rn episodes observed at Crozet Island in the Indian Ocean, demonstrating that they can resolve the synoptic-scale transport of continental plumes with no significant numerical diffusion. Large differences between models are found in the rates of meridional transport in the upper troposphere (interhemispheric exchange, exchange between tropics and high latitudes). The four two-dimensional models which participated in the intercomparison tend to underestimate the rate of vertical transport from the lower to the upper troposphere but show concentrations of 222Rn in the lower troposphere that are comparable to the zonal mean values in the three-dimensional models.
274 citations
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TL;DR: The effect of large-scale atmospheric pressure changes on the 222Rn flux across the soil-air interface is investigated in this paper, where a simple model of molecular diffusion combined with pressure-induced transport in the soil has been confirmed by laboratory experiments using a vertical column of 226Ra-bearing sand.
Abstract: The effect of large-scale atmospheric pressure changes on the 222Rn flux across the soil-air interface is investigated. Field data collected during 1972 and 1973 show that pressure changes of 1–2% associated with the passage of frontal systems produce changes in the 222Rn flux from 20 to 60%, depending upon the rate of change of pressure and its duration. A simple model of molecular diffusion combined with pressure-induced transport in the soil has been confirmed by laboratory experiments using a vertical column of 226Ra-bearing sand. On the basis of this model, pressure changes of 10–20 mbar occurring over a period of 1–2 days produce Darcy velocities of the order of 10−4 cm s−1 near the surface of a soil having a permeability of 10−8 cm2. The corresponding variations in the 222Rn flux predicted by the model are in agreement with those observed from valley alluvium in central New Mexico.
261 citations
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