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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] The dust emission simulated within the up-to-date global and regional models differs by almost an order of magnitude. The models are tuned to reproduce the observed aerosol optical depth (AOD) that, with some caveats, reflects the dust mass retained in the atmosphere. However, the amount of dust suspended in the atmosphere is controlled independently by the dust emission and deposition; therefore, only AOD observations are insufficient to constrain both these processes. To calculate the dust emission over the Middle East (ME), in this study, we employ dust deposition observations, AERONET AOD, micro-pulse lidar, and satellite observations to constrain the WRF-Chem simulations. The dust deposition is measured on a monthly bases for 2015-2019 using passive samplers over six sites over land and the sea. We compare the WRF-Chem simulations, conducted with 10-km grid spacing, with the recent MERRA-2 and CAMS reanalysis. WRF-Chem is configured with the GOCART dust scheme. We calculate the meteorological and aerosol initial and boundary conditions using the MERRA-2 reanalysis. We evaluated the dust regional mass balance controlled by emission, deposition, and cross-boundary transport. The smallest dust particles are transported at vast distances while the heaviest ones deposit inside of the domain. Since the model accounts for dust particles with radii<10 um, we process the deposition samples to extract the weight of particles smaller than 10 um. WRF-Chem was tuned to reproduce the observed AOD and monthly deposition of dust particles with radii < 10 um. We found that the ME dust emission comprises about 30% of the global annual dust emission. MERRA-2 underestimates the ME dust emission by about 15%.
[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] 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] 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] In France, Germany, Sweden and Switzerland, the licensing authorities have decided to equip nuclear reactor containments with a filter venting system to ensure survival of the containment after postulated severe nuclear accidents. This is a curious paradox. For years, the established wisdom was unambiguously 'Keep the containment tight. It's the ultimate barrier'. Three Mile Island seemed to prove the point. Yet, an old mechanical engineer's rule is 'Every pressure vessel must have a safety valve'. Filtered containment venting attemps to reconcile these two conflicting objectives by allowing a filtered pressure relief after the accident, in order to prevent containment failure due to overpressure, while keeping the release within acceptable limits. Achieving this dual objective is a matter of proper timing, i.e. pressure relief, not too early, not too late. (orig.)
[de]In Schweden, Frankreich, Deutschland und der Schweiz haben die Genehmigungsbehoerden entschieden, dass die Sicherheitshuellen (Containments) der Kernreaktoren mit einem Druckentlastungssystem auszuruesten seien. Damit soll auch nach einem schweren Stoerfall die Funktion der Sicherheitshuelle gewaehrleistet bleiben. Dies scheint ein Widerspruch. Ueber Jahre lautete die Regel: 'Haltet das Containment dicht. Es bildet die letzte Barriere.' Three Mile Island schien diese These zu bestaetigen. Auf der anderen Seite besagt ein alter Leitsatz der Maschinentechnik: 'Jeder Druckbehaelter muss mit einem Sicherheitsventil ausgeruestet sein.' Die Druckentlastung ueber Filter bringt diese beiden in sich widerspruechlichen Zielsetzungen miteinander in Einklang. Das Containment wird durch die Druckentlastung vor einem Versagen durch Ueberdruck geschuetzt, und die Abgaben an die Umwelt bleiben innerhalb der gesetzten Grenzen. Diese zwei Ziele werden erreicht durch die Wahl des richtigen Zeitpunkts der Druckentlastung; d.h. nicht zu frueh, aber auch nicht zu spaet. (orig.)