Analysis of radon origin by backward atmospheric transport modelling

This work shows how ambient radon concentrations measured at Cabauw station in central Netherlands are influenced by transport from different regions under typical transport conditions occurring during April and November, 2007 by means of atmospheric Lagrangian particle dispersion modelling in a receptor-oriented approach. Four specific regions have been isolated to assess their contribution to the modelled radon ambient concentrations at Cabauw, and two different radon flux assumptions. Westerly flows coming from the ocean are poor in radon and do not increase radon air concentrations unless there is some fetch over the British Isles. Continental transport, mainly from eastern and southern Europe, significantly increases radon background concentrations, reaching increments of 3 Bq m^?3. A constant 0.66 atoms cm^?2 s^?1 radon flux over land and zero over water bodies is a good approximation for the source term in order to study regional contributions and modulation of the radon background.     

An atmospheric stability index based on radon progeny measurements for the evaluation of primary urban pollution

An atmospheric stability index for the evaluation of urban primary pollution, based on the elaboration of natural radioactivity data yielded by a stability monitor, has been developed. The instrument determines the atmospheric concentration of the short-lived decay products of radon, whose emanation rate can be assumed to be constant in the time and space scale of observation. The index gives information about the dilution properties of the lower boundary layer and allows to highlight the relevant role of the dilution factor in determining primary pollution events.The atmospheric stability indices have been calculated during a 1-yr study carried out in the urban area of Rome (October 1999–September 2000). On the basis of the index, every day of the period has been classified in terms of intensity of a potential primary pollution event. The comparison between this classification and the real concentration value of primary pollutants, measured in the background urban station of Rome, yielded very good results. This shows that the index constitutes a powerful and valuable tool for describing primary pollution events in urban areas and confirms that the role played by the mixing properties of the lower boundary layer is essential in determining primary pollution in urban areas.     

An automated systems for air sampling with annular denuder systems at a remote site

An automated air sampling system has been designed for use with the annular denuder system (ADS). The automated air sampling system allows for accurate measurements of air volume and day-night sampling while preventing the accumulation of moisture within the ADS caused by condensation or cloud events. The sampling system consists of air flow, monitoring and control subsystems. Calibration of the sampling system against a Hoffer turbine flow meter indicated accurate measurement of air flow volumes. Field testing and preliminary data have shown that the sampling system functions well in a remote mountain forest site, and was relatively unaffected by condensation, fog, or cloud events.     

Investigation of the influences of atmospheric conditions on the variability of radon and radon progeny in buildings

Analysis of time-series data sets, collected in vernacular buildings and workplaces linked with radium source bedrock has identified a number of internal and external pressure characteristics linking meteorological parameters with the variability of radon gas and its progeny. The cellars in these buildings are excavated from the bedrock associated with the radium source and have relatively high levels of radon concentration along with largely stable microclimatic conditions, which differ from those of the buildings’ ground and upper levels. In workplace environments cyclical characteristics are apparent, associated with heating and ventilation related to working hours. Comparative radon concentration data, collected within buildings and similarities identified between buildings, suggest the need to distinguish between short and longer-term influences. From a range of comparative data studied, water vapour pressure, a partial pressure of barometric pressure, is indicated as a principal determinant of the short-term variability of radon gas concentrations, with barometric pressure determining the trend or general longer term level, both linked to temperature. Wind speed appears to have the potential for a dual influence on radon variability: directly, through wind pressure differences and indirectly, through changes to the water vapour component.     

An automated overlying water-renewal system for sediment toxicity studies

An automated water-renewal toxicity test system is described for exposing benthic invertebrates to whole sediments. The system will intermittently deliver laboratory or on-site water for overlying water replacement in sediment exposures. A range of cycle rates can be used to produce different volume additions of overlying water per day to exposure chambers. The system can be used with six different treatments and eight replicates per treatment producing 48 exposure chambers. Three formulated sediments with variable organic carbon (1.5%, 7.5%) and sand (14%, 63%) content were prepared to test the system exposing amphipods, Hyalella azteca and midges, Chironomus tentans in 10 day whole sediment tests. Intermittent water flow was used with a 90 min cycle time to create two volume additions of laboratory water per 24 h in exposure chambers (180 ml sediment, 320 ml water). Overlying water quality conditions, and survival and growth of both species were consistent and within acceptable limits for the testing requirements of the U.S. EPA guidelines for sediments with freshwater invertebrates.     

改进GC/ECD法连续测定大气中的CFCs

基于气相色谱仪 (GC)和电子捕获检测器 (ECD) ,设计了一种连续测量大气中痕量氯氟烃的自动系统。系统色谱基线稳定 ,分离效果好 ,定性、定量准确可靠 ,系统高度自动化 ,长期运行无需人值守 ,自动校正数据 ,定时进行严格的质量控制 ;系统具有较高的现场测量频率 (6次 /h) ,改进的反吹 /外切设计使CFCs色谱峰不再受氧峰的干扰 ,大大延长了检测器的寿命 ,使长期连续观测成为可能。系统设计在分离效果方面优于世界气象组织 (WMO)全球大气监测网 (GAW )目前所使用的测量大气本底CFCs的方法 ,采用美国EPA认可的标气 ,外标工作曲线法测定大气CFCs的浓度 ,最低检测限可达1pL/L ,检测精密度小于 1 % ,准确度在± 3%之内 ,可用于我国本底大气观测站对CFCs的连续测定     

改进GC/FID法连续观测大气中CO浓度

改进装配有氢火焰离子化检测器(即FID)的气相色谱仪(GC),可连续监测大气中痕量气体CO浓度.本系统采用单阀双柱反吹进样技术,优选前置柱能更有效地剔除杂质,提高了分析柱效率,保持色谱基线平稳,提高分辨率和定量分析的准确率.优化后的气路设计与色谱柱的改进,使GC/FID对CO的最低检出限达到10×10-9、精密度误差小于2%,准确度在±2%之内.将气相色谱与动态气体稀释仪耦合使系统能够自动进行工作曲线校准,系统自动采样、分析和标定,无需人员职守.对北京大气CO连续观测结果表明,北京大气CO浓度变化受气象要素与排放源双重控制.     

压差法大气污染物采样误差分析

智能综合大气采样器能对空气中总悬浮微粒及有害气体进行采样,使用孔板压差流量计和转子流量计分别进行气体流量测量。依据智能大气综合采样器采样原理,推导采样器孔板压差流量计理论流量公式,并通过实测数据对流量计计量公式进行验证。在此基础上,从3个方面分析大气采样器计量误差来源,并针对传感器压力取值误差,设计并验证增加采样次数取均值可以降低误差值;对因环境因素引起的误差,提出3种降低大气采样器采样误差的方法。     

Intercomparison of methods for sampling and analysis of atmospheric mercury species

An intercomparison for sampling and analysis of atmospheric mercury species was held in Tuscany, June 1998. Methods for sampling and analysis of total gaseous mercury (TGM), reactive gaseous mercury (RGM) and total particulate mercury (TPM) were used in parallel sampling over a period of 4 days. The results show that the different methods employed for TGM compared well whereas RGM and TPM showed a somewhat higher variability. Measurement results of RGM and TPM improved over the time period indicating that activities at the sampling site during set-up and initial sampling affected the results. Especially the TPM measurement results were affected. Additional parallel sampling was performed for two of the TPM methods under more controlled conditions which yielded more comparable results.     

Micrometeorological influences and surface layer radon ion production: Consequences for the atmospheric electric field

Variation of surface electric field with special thrust to atmospheric inversion condition is studied for the tropical station Pune (18°32′N, 73°51′E, 550 m ASL) for the year 1993 considering average meteorological conditions. The study aims to understand the relative effect of space charge density variation modulated by vertical temperature gradient (lapse rate) Vs conductivity variations controlled by radionuclide concentration on modification of electric field close to surface. Electric field is predominantly controlled by lapse rate (space charge density variation) and radon progeny concentration (conductivity modification) in summer and winter respectively. An empirical relation developed elsewhere is evaluated for the present observations.     

Evaluation of the measurement uncertainty in automated long-term sampling of PCDD/PCDFs

Since the publication of the first version of European standard EN-1948 in 1996, long-term sampling equipment has been improved to a high standard for the sampling and analysis of polychlorodibenzo-p-dioxin (PCDD)/polychlorodibenzofuran (PCDF) emissions from industrial sources. The current automated PCDD/PCDF sampling systems enable to extend the measurement time from 6–8 h to 15–30 days in order to have data values better representative of the real pollutant emission of the plant in the long period. EN-1948:2006 is still the European technical reference standard for the determination of PCDD/PCDF from stationary source emissions. In this paper, a methodology to estimate the measurement uncertainty of long-term automated sampling is presented. The methodology has been tested on a set of high concentration sampling data resulting from a specific experience; it is proposed with the intent that it is to be applied on further similar studies and generalized. A comparison between short-term sampling data resulting from manual and automated parallel measurements has been considered also in order to verify the feasibility and usefulness of automated systems and to establish correlations between results of the two methods to use a manual method for calibration of automatic long-term one. The uncertainty components of the manual method are analyzed, following the requirements of EN-1948-3:2006, allowing to have a preliminary evaluation of the corresponding uncertainty components of the automated system. Then, a comparison between experimental data coming from parallel sampling campaigns carried out in short- and long-term sampling periods is realized. Long-term sampling is more reliable to monitor PCDD/PCDF emissions than occasional short-term sampling. Automated sampling systems can assure very useful emission data both in short and long sampling periods. Despite this, due to the different application of the long-term sampling systems, the automated results could not be directly compared with manual results, not even in terms of measurement uncertainty. This investigation focuses on both uncertainty and repeatability of the automated sampling method. The standard 20988, developed by Internarional Organization of Standardization (ISO) can be used to estimate the measurement uncertainty. The results confirm that the uncertainties of manual and automated methods are comparable. At the same time, it is not appropriate to consider the manual method as a reference for the evaluation of the uncertainty of the automated sampling system, due to the high variability of both systems.     

An aerosol injection and outdoor chamber system for the study of atmospheric gasparticle reactions

A system for the study of reactions between particle bound organic compounds and gaseous pollutants is described. The system is based on two 25 m³ outdoor smog chambers and associated equipment. Injection of sub-μm diameter carbon black particles is achieved using a liquid nitrogen based injection system. Suspended mass half life in the chamber is increased from 0.8 to 5.8 h by the use of a bipolar ion atmosphere. Particle concentrations and size distributions are shown to be similar to those obtained from wood combustion.     

An automated test for measuring polymer biodegradation

The biodegradability of polymer materials as evaluated by the modified Sturm test is labor-intensive, cumbersome and costly and also tends to cumulate errors. An automated system for the measurement of carbon dioxide would overcome many of these disadvantages. We describe here a method in which CO2 was determined by IR spectroscopy. We compared the results with those from trapping CO2 in a solution of barium hydroxide (Ba(OH)2) followed by manual titration. The automated system was more reproducible, less costly and more compact. The automated system could also be employed to measure the biodegradability of other substances such as oils and detergents.     

Reduction of sampling and analytical errors for electron microscopic analysis of atmospheric aerosols

Electron microscopy-energy dispersive spectroscopy (EM/EDS) can be used to determine the elemental composition of individual particles. However, the accuracy with which atmospheric particle compositions can be quantitatively determined is not well understood. In this work we explore sources of sampling and analytical bias and methods of reducing bias. Sulfuric acid [H₂SO₄] and ammonium sulfate [(NH₄)₂SO₄] particles were collected on beryllium, silicon, and carbon substrates with similar deposition densities. While [(NH₄)₂SO₄] particles were observed on all substrates, [H₂SO₄] and ammonia-treated [H₂SO₄] particles could not be found on beryllium substrates. Interactions between the substrate and sulfuric acid particles are implicated. When measured with EM/EDS, [H₂SO₄] particles exposed to ammonia overnight were found having lower beam damage rates (0.000 ± 0.002 fraction s⁻¹) than those without any treatment (0.023 ± 0.006 fraction s⁻¹) For laboratory-generated [C₁₀H₆(SO₃Na)₂] particles, the composition determined using the experimental k-factors evaluated from independent particle standards of similar composition and size shows an error less than 20% for all constituents, while greater than 78% errors were found when k-factors were calculated from the theory. This study suggests (1) that sulfate beam damage can be reduced by exposure of atmospheric particle samples to ammonia before analysis, (2) that beryllium is not a suitable substrate for atmospheric particle analysis, and (3) calibration (k-factor determination) using particle standards of similar size and composition to particles present in the atmosphere shows promise as a way of improving the accuracy of quantitative EM analysis.     

A passive sampling method for radiocarbon analysis of atmospheric CO2 using molecular sieve

Radiocarbon (¹⁴C) analysis of atmospheric CO₂ can provide information on CO₂ sources and is potentially valuable for validating inventories of fossil fuel-derived CO₂ emissions to the atmosphere. We tested zeolite molecular sieve cartridges, in both field and laboratory experiments, for passively collecting atmospheric CO₂. Cartridges were exposed to the free atmosphere in two configurations which controlled CO₂ trapping rate, allowing collection of sufficient CO₂ in between 1.5 and 10 months at current levels. ¹⁴C results for passive samples were within measurement uncertainty of samples collected using a pump-based system, showing that the method collected samples with ¹⁴C contents representative of the atmosphere. δ¹³C analysis confirmed that the cartridges collected representative CO₂ samples, however, fractionation during passive trapping means that δ¹³C values need to be adjusted by an amount which we have quantified. Trapping rate was proportional to atmospheric CO₂ concentration, and was not affected by exposure time unless this exceeded a threshold. Passive sampling using molecular sieve cartridges provides an easy and reliable method to collect atmospheric CO₂ for ¹⁴C analysis.     

Long-term automated sampling of PCDD/PCDF flue gas: current status and critical issues

After entry into force of the Stockholm Convention and Aarhus Protocol and in order to implement the upcoming European legal background, the European countries are asked to apply control measures to reduce the release of persistent organic pollutants (POPs) such as dioxins and furans (PCDD/PCDF) and polychlorinated biphenyls as well as to establish POPs release inventories. In this perspective, development of measuring techniques of emissions is a focal issue in acquiring useful information. In this paper, results of various measurement campaigns at different municipal waste incineration (MWI) plants using long-term automated sampling of PCDD/PCDF are presented. The samples collected from both manual and automated campaigns were analyzed following the European Standard EN-1948:2006 by high-resolution gas chromatograph/high-resolution mass spectrometer. Performances of two different commercial systems have been investigated. Anomalous values occurred during one long-term campaign (22.16 pg I-toxic equivalent (TEQ)/Nm(3)), compared to average values (4-5 pg I-TEQ/Nm(3)) of the MWI. At this maximum value, a main occurrence of abnormal and instable operating conditions has been found. Sampling based on long-term basis was found to be more reliable to monitor PCDD/PCDF emissions than occasional short-term sampling. Nevertheless, the results of long-term campaigns demonstrate that emission levels detected in 15-30 days campaigns, when unsteady operating conditions can occur, as start-up and shut down, are not immediately comparable to the typical levels in a 6-8 h, when operating conditions are generally stable. Moreover, there are often differences observed in the congener profiles between short- and long-term campaigns.     

Duplicate sampling reproducibility of atmospheric residues of herbicides for paired pan and high-volume air samplers

The reproducibility of collection of atmospheric residues of the herbicides 2,4-D and triallate as bulk (wet plus dry) deposition samples by paired pan samplers and as particulate (filter) and vapour (PUF/XAD-2 resin cartridge) samples by paired high-volume air samplers was determined. Variability of herbicide concentrations in paired bulk deposition samples was within 25% for 65 and 80% of the samples for 2,4-D and triallate, respectively, with approximately 90% of the paired samples being within a factor of 2 for both herbicides. The vapour samples of 2,4-D and triallate showed similar reproducibilities. The highest reproducibility was observed for the filter samples with 92% of the paired data sets for 2,4-D being within 25% variability. No triallate was detected in the filter samples.     

Studies on automated survey system of environmental chemicals by gas chromatography-mass spectrometry-computer III. Construction of an automated survey system and its application

An automated survey system on the chemicals in environments by a gas chromatography-mass spectrometry-computer system has been constructed of Three Dimensional Mass Chromatography, Modified Probability Based Matching method, and Self Training Interpretive and Retrieval method. And it was applied to analyze environmental materials, with interesting results.