Aerosol Trapping Research Articles

Radioactive nuclides as tracers of environmental processes

Relatively short-lived radioactive nuclides of cosmogenic origin, such as7Be (T1/2=53.3 d),32P (14.3 d),33P (25.3 d),35S (87.4 d) as well as22Na (2.6 y) have come to be recognized as potential tools to trace environmental processes, such as precipitation, washout (precipitation scavenging), resuspension, atmospheric particle deposition and deposition patterns of airborne contaminants, aerosol deposition and aerosol trapping by above ground vegetation (air-to-vegetation transfer). Of the above radionuclides,7Be as well as210Pb of terrestrial origin and137Cs, a fission product radionuclide, are commonly used for determining the atmospheric particle deposition parameters. It was found that the deposition velocity of7Be-associated aerosol particles varied from 0.3 to 0.8 cm. s-1(average 0.5 cm. s-1), the washout ratio for7Be varied from 103 to 375 (average 144), the resuspension factor for the7Be-associated particles varied from 1.6. 10-4to 4.2. 10-4m-1(average 2.3. 10-4m-1) and the air-to-vegetation transfer rate for7Be varied from 5258 to 16180 m3.kg-1(average 9856 m3.kg-1) for grass, gramineae or poaceae the species. For the137Cs-associated aerosol particles the deposition velocity varied from 1.3 to 6.3 cm. s-1(average 3.4 cm. s-1), the washout ratio for137Cs varied from 284 to 3810 (average 1295), the resuspension factor for the137Cs-associated aerosol particles varied from 0.1. 10-4to 1.2. 10-4m-1(average 0.6. 10-4m-1) and the air-to-vegetation transfer rate for137Cs varied from 39638 to 345279 m3.kg-1(average 181197 m3.kg-1) for grass, gramineae or poaceaethe species.

Closed tube sample introduction for gas chromatography–ion mobility spectrometry analysis of water contaminated with a chemical warfare agent surrogate compound

Ion mobility spectrometry (IMS) is a proven technology for detection of vapor phase chemical warfare agents. The technology is suitable for field portable instrumentation due to its small size, high sensitivity, speed of analysis, and low power consumption. However, it suffers from a limited dynamic range and potential difficulties in identifying compounds in complex matrices. The use of gas chromatography (GC) coupled to IMS can overcome the difficulty of chemical identification in mixtures by separating the sample into individual components before detection. Using this approach, IMS technology has previously been adapted to detect biological aerosols using an open tube pyrolyzer and a short GC column (Py-GC–IMS). The open sample introduction tube of a Py-GC–IMS instrument would be a convenient configuration to accept aerosol particulates, and while viewed as needed for aerosol trapping, is not optimal for liquid chemical analyses. To examine the usefulness of an existing Py-GC–IMS system for analysis of chemicals in water, an existing open-port sample interface was replaced with a septum-equipped closed tube injector to contain analyte vapors resulting from liquid injection. Tributylphosphate (TBP) was used as a surrogate chemical warfare agent, and aqueous injections into both closed and open tube assemblies were performed. Sample introduction into the closed tube inlet was also accomplished using solid phase microextraction (SPME) preconcentration. The limit of detection for TBP using an open tube, closed tube, and closed tube configuration with SPME sample introduction was 0.980, 0.196, and 0.0098 mg/L, respectively.

ARTIST: introduction and first results

Aerosol Trapping In a Steam Generator (ARTIST) is a seven-phase international project (2003–2007) which investigates aerosol and droplet retention in a model steam generator under dry, wet and accident management conditions, respectively. The test section is comprised of a scaled steam generator tube bundle consisting of 270 tubes and three stages, one 1:1 separator unit, and one 1:1 dryer unit. As a prelude to the ARTIST project, four tests are conducted in the ARTIST bundle within the 5th EU FWP SGTR. These first tests address aerosol deposition phenomena on two different scales: near the tube break, where the gas velocities are sonic, and far away from the break, where the flow velocities are three orders of magnitude lower. With a dry bundle and the full flow representing the break stage conditions, there is strong evidence that the TiO 2 aerosols used (AMMD 2–4 μm, 32 nm primary particles) disintegrate into much smaller particles because of the sonic conditions at the break, hence promoting particle escape from the secondary and lowering the overall DF, which is found to be between 2.5 and 3. With a dry bundle and a small flow reproducing the far-field velocities, the overall bundle DF is of the order of 5, implying a DF of about 1.9 per stage. Extrapolating the results of the dry tests, it turns out that for steam generators with nine or more stages, it is expected that substantial DF’s could be achieved when the break is located near the tube sheet region. In addition, better decontamination is expected using more representative proxies of severe accident aerosols (sticky, multi-component particles), a topic which is yet to be investigated. When the bundle is flooded, the DF is between 45 and 5740, depending on the mass flow rate, the steam content, and the water submergence. The presence of steam in the carrier gas and subsequent condensation inside the broken tube causes aerosol deposition and blockages near the break, leading to an increase in the primary pressure. This has implications for real plant conditions, as aerosol deposits inside the broken tube will cause more flow to be diverted to the intact tubes, with a corresponding reduction in the source term to the secondary.

2411 格納容器貫通部のリーク条件と FP エアロゾル捕集効果

2411 格納容器貫通部のリーク条件と FP エアロゾル捕集効果

In situ size determination of single levitated solid aerosols

An insitu sizing technique for single levitated solid aerosols is reported. The particle size is investigated in micrometre-sized sodium chloride particles, where the size and state of matter depend strongly on the ambient humidity. The experimental approach makes use of elastic light scattering from the particles that are levitated in an electrodynamic aerosol trap, where the patterns of scattered light are fast Fourier transformed for size determination. It is shown that this approach requires for solid particles short detection times of the scattered light, typically of the order of 0.1 ms, so that the solid particle can be treated as almost stationary in the trap. Size calibration of the fast Fourier transforms of the light scattering patterns is obtained by correlating the space frequency with the equivalent edge length. Deviations from a linear correlation are interpreted as evidence for the occurrence of non-cubic crystal shapes. This result is in agreement with additional experiments using conventional light microscopy.

Turbulent deposition and trapping of aerosols at a wall

The trajectories of aerosols are computed in a high-resolution direct numerical simulation of turbulent flow in a vertical channel. The aerosol equation of motion includes only a Stokes drag force and the influence of the aerosols on the gas flow is assumed to be negligible. Since the flow is vertical, aerosols deposit as a consequence of the turbulent fluctuations and their own inertia. It is shown that the eddies which are responsible for aerosol deposition are the same eddies that control turbulence production. Typical aerosol trajectories are shown and related to eddy structure. A free-flight theory suggested by Friedlander and Johnstone [Ind. Eng. Chem. 49, 1151 (1957)] is found to be based on reasonable assumptions about typical velocities of depositing aerosols as they pass through the viscous sublayer, but the theory is shown to be deficient in other respects. The distribution of normal velocities of the aerosols that deposit is compared to the distribution of fluid particle velocities in the viscous sublayer and some support is found for the notion that the probability distribution of Eulerian velocities may be useful in predicting deposition.

Case report: Freebased cocaine smoking and reactive airway disease

The case of a 19-year-old white female who presented with marked respiratory distress and pleuritic chest pain following freebased cocaine smoking is presented. A ventilation-perfusion scan revealed radioactive aerosol trapping in the large airways with multiple ventilation defects of the small airways, a finding compatible with reactive airway disease of the large airways and concomitant mucous plugging of the small airways. Freebased cocaine, impurities of the freebasing process, or admixtures to the freebased cocaine provided prior to smoking, are proposed as possible etiologies in what appears to be a condition of environmentally induced reactive airway disease, a previously unreported effect of cocaine use.

Use of a thermospray nebuliser as a sample introduction system for inductively coupled plasma atomic emission spectrometry

A thermospray nebuliser has been used for sample introduction into the ICP and the experimental set-up of the system is described in this paper. The operating conditions of the thermospray nebuliser have been optimised to obtain the lowest detection limits. The following features were studied: sensitivity, short- and long-term stability, detection limits for 14 elements and matrix effects on eight elements caused by 1 g l–1 NaCl. In all instances, a comparison was made between the thermospray nebuliser and a pneumatic nebuliser. Finally, the mass transport efficiency of both nebuliser systems was measured for four elements using direct aerosol trapping.

Application of pyrolysis—gas chromatography with a multidetector to aerosol analysis

A technique for aerosol detection and identification by pyrolysis—gas chromatography is presented. The aerosols were collected on powdered materials packed in a filtering tube and then pyrolyzed by heating the tube. A sufficiently complete trapping of aerosols was provided by crushed silica glass; both aerosols and vapours were readily collected by adsorbents, such as molecular sieves. Identification was carried out using a multidetector with three recording channels.