Results 1 - 10 of 20891
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[en] Highlights of current dust and mineral aerosol modeling activities at the National Centers for Environmental Prediction (NCEP), and projections for the future are presented. On the atmospheric modeling side, current activities are reviewed on the development of a unified nonhydrostatic atmospheric model that can be used for driving dust and aerosol models on a wide range of scales extending from meso to global. Finally, some of the outstanding problems associated with modeling of the transport of atmospheric constituents are discussed.
[en] Objective: To overcoming the pungent smell when DOP generates aerosol and the risk of potential carcinogen for HEPA leak rate testing in nuclear ventilation system. Methods: The closed cup method is used to measure the flash point about PAO4 and DOP. Mixing uniformity testing and in-site leak rate testing are done according to the EJ/T 79l standard. Results: The flash point of PAO4 is higher than the flash point of DOP. It Is stable when PAO4 generates aerosol. The leak rate testing result is coincident. Conclusion: PAO4 is deserved to popularize for HFPA leak rate testing in nuclear ventilation system. (authors)
[en] In the past the study of aerosol filtration by fibrous filter mats has concentrated on the elucidation of the mechanisms of filtration, delineating the fractional contributions of diffusion, impaction, and inertia to the overall filtration efficiency. A conceptual approach is offered which would study the kinetics of aerosol filtration, concentrating on determining the aerosol filtration capacity and aerosol filtration rate constant of the filter mat. Since all physical systems can be characterized by two fundamental properties, namely a quantity factor and an intensity factor, it is expected that the filtration capacity and filtration rate constant will relate respectively to these two properties. Using the basic relationships originally derived from a continuity equation of mass balance, and a methodology analogous to that used to study the kinetics of gas adsorption, an equation was developed which should permit the determination of the aerosol filtration capacity and rate constant values for various filter mats from a series of life-thickness plots for the mats. By plotting the protective life in minutes, required to produce a chosen fractional exit to inlet aerosol penetration ratio, against the mat weight or thickness, a straight line should result from which one should be able to determine respectively the filtration capacity and filtration rate constant of the mat. The effect of superficial linear velocity on the capacity and rate constant parameters can also be determined by the same methodology. Aerosol and filter mat variations in size and type can be factored into a test program matrix to fully assess the kinetics of aerosol filtration
[en] Since April 1, 1982, the Aussenstelle at Freiburg/Schauinsland of the Max-Planck-Institut fuer Kernphysik is incorporated into the Bundesamt fuer Zivilschutz at Bonn. This report summarizes the past and present investigations performed at the Aussenstelle. (orig.)
[en] Regional studies focusing on the role of atmospheric nanoparticles in climate change have gained impetus in the last decade. Several multi-institutional studies involving measurement of nanoparticles with several kinds of instruments are on the rise. It is important to harmonize these measurements as the instruments may work on different techniques or principles and are developed by different manufacturers. Scanning mobility particle sizers (SMPS) are often used to measure size distribution of nanoparticles in the airborne phase. Two such commercially available instruments namely, GRIMM and TSI-SMPS have been compared for ambient and laboratory generated conditions. A stand-alone condensation particle counter (CPC) of TSI make was used as a reference for particle concentration measurements. The consistency of the results in terms of mean size and geometric standard deviation was seen to be excellent for both the SMPSs, with GRIMM always showing slightly (approximately 10 %) lower mean size. The integrated number concentration from GRIMM-SMPS was seen to be closer to stand-alone reference CPC compared to TSI-SMPS, for an ambient overnight comparison. However, a concentration-dependent response, i.e. the variations between the two instruments increasing with the concentration, was observed and possible reasons for this have been suggested. A separate experiment was performed for studying the modifying effect of diffusion dryer and sheath air dryer on the measured aerosol size spectra. A significant hygroscopic growth was noted when diffusion dryer was attached to one of the SMPS. The introduction of sheath air dryer in GRIMM-SMPS produced a significant shift towards lower mean size. These results have been compared and discussed with the recent inter-comparison results to strengthen and harmonize the measurement protocols.
[en] Determination of aerosol particle size distribution has been done using a low pressure Andersen's cascade impactor with 13 stages. The aerosol has been sampled with flow rate of aerosol sampling of 28.3 Ipm. Preliminary study result shows that aerosol in the simulation chamber was spread in monomodal distribution with Mass Median Aerodynamic Diameter of 4.9 μm. The aerosol measurement in Japan Power Demonstration Reactor has been spread in trimodal distribution with Activity Median Aerodynamic Diameter equal to 13.3 μm. The use of mylar as impaction plate instead of aluminum foil gives good result
[en] Stratospheric aerosol injection (SAI) is a climate engineering method that is reputed to be very effective in cooling the planet but is also thought to involve major risks and side effects. As a new option in the bid to counter climate change, it has attracted an increasing amount of research and the debate on its potential gained momentum after it was referred to in the 5th IPCC assessment report (IPCC 2013). One major objection to SAI and the research done on it is that it could undermine commitment to the mitigation of greenhouse gases. Policymakers, interest groups or individuals might wrongly perceive SAI as an easy fix for climate change and accordingly reduce their mitigation efforts. This is the first study to provide an empirical evaluation of this claim for individuals. In a large-scale framed field experiment with more than 650 participants, we provide evidence that people do not back-pedal on mitigation when they are told that the climate change problem could be partly addressed via SAI. Instead, we observe that people who have been informed about SAI mitigate more than people who have not. Our data suggest that the increase is driven by a perception of SAI as potential threat. (letter)
[en] In this report a model for simulating aerosol cluster impact with rigid walls is presented. The model is based on JKR adhesion theory and is implemented as an enhancement to the granular (DEM) package within the LAMMPS code. The theory behind the model is outlined and preliminary results are shown. Modeling the interactions of small particles is relevant to a number of applications (e.g., soils, powders, colloidal suspensions, etc.). Modeling the behavior of aerosol particles during agglomeration and cluster dynamics upon impact with a wall is of particular interest. In this report we describe preliminary efforts to develop and implement physical models for aerosol particle interactions. Future work will consist of deploying these models to simulate aerosol cluster behavior upon impact with a rigid wall for the purpose of developing relationships for impact speed and probability of stick/bounce/break-up as well as to assess the distribution of cluster sizes if break-up occurs. These relationships will be developed consistent with the need for inputs into system-level codes. Section 2 gives background and details on the physical model as well as implementations issues. Section 3 presents some preliminary results which lead to discussion in Section 4 of future plans.