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261.
Wind erosion selectively winnows the fine, most chemically concentrated portions of surface soils and results in the inter-regional
transport of fugitive dust containing plant nutrients, trace elements and other soil-borne contaminants. We sampled and analyzed
surface soils, sediments in transport over eroding fields, and attic dust from a small area of the Southern High Plains of
Texas to characterize the physical nature and chemical constituents of these materials and to investigate techniques that
would allow relatively rapid, low cost techniques for estimating the chemical constituents of fugitive dust from an eroding
field. From chemical analyses of actively eroding sediments, it would appear that Ca is the only chemical species that is
enriched more than others during the process of fugitive dust production. We found surface soil sieved to produce a sub-sample
with particle diameters in the range of 53–74 μm to be a reasonably good surrogate for fugitive dust very near the source
field, that sieved sub-samples with particle diameters <10 μm have a crustal enrichment factor of approximately 6, and that
this factor, multiplied by the chemical contents of source soils, may be a reasonable estimator of fugitive PM10 chemistry from the soils of interest. We also found that dust from tractor air cleaners provided a good surrogate for dust
entrained by tillage and harvesting operations if the chemical species resulting from engine wear and exhaust were removed
from the data set or scaled back to the average of enrichment factors noted for chemical species with no known anthropogenic
sources. Chemical analyses of dust samples collected from attics approximately 4 km from the nearest source fields indicated
that anthropogenic sources of several environmentally important nutrient and trace element species are much larger contributors,
by up to nearly two orders of magnitude, to atmospheric loading and subsequent deposition than fugitive dust from eroding
soils. 相似文献
262.
This paper provides baseline information about the total annual dust fall, and its constituents and seasonal variation, from a sub-tropical opencast coalmine area in Bina, India. Dust samples were collected monthly for 2 years (June 2002-May 2004) from five sampling sites in the region and analyzed in the laboratory for water-soluble and -insoluble matter. Water-insoluble components constituted the major fraction of the total annual dust fall. Two-way ANOVA indicated significant variations in dust fall at different sites, over the months and in their interactions. The dust deposition rate was highest during summer (March-June), followed by winter (November-February) and lowest in the rainy season (July-October). Maximum dust fall was observed near the coal handling plant (at site 2) followed by the receiving pit of the coal handling plant (site 3), near the main sub-station (site 4), Jawahar colony (site 1) and Gharasari village (site 5). An inverse and significant relation was observed between dust fall and precipitation. Our studies have shown that the main residential areas are experiencing higher levels of dust fall which makes them unsuitable for living. We suggest that residential areas should be moved farther away from the mining area in the opposite direction of prevalent winds. 相似文献
263.
264.
甘肃干旱、半干旱地区尘类污染特征分析 总被引:3,自引:0,他引:3
本文用近10年来TSP、降尘监测数据对甘肃省干旱、半干旱地区尘类污染进行了较系统、全面地分析。总结出省内不同区域内尘污染时空分布特征,进一步阐明尘类污染是影响我省城市大气环境的重要指标。 相似文献
265.
The production of materials with dimensions in the nanometre range has continued to increase in recent years. In order to ensure safety when handling these products, the hazard potential of such innovative materials must be known. While several studies have already investigated the effects of explosions (such as maximum explosion pressure and maximum pressure rise) of powders with primary particles in the nanometre range, little is known about the ignition temperatures and flame velocities. Therefore, the minimum ignition temperature (MIT) of metallic nano powders (aluminium, iron, copper and zinc) was determined experimentally in a so called Godbert-Greenwald (GG) oven. Furthermore, the flame velocities were determined in a vertical tube. In order to better classify the test results, the tested samples were characterised in detail and the lower explosion limits of the tested dust samples were determined. Values for the burning velocity of aluminium nano powders are higher compared to values of micrometre powders (from literature). While MIT of nanometre aluminium powders is within the range of micrometre samples, MIT of zinc and copper nano powders is lower than values reported in literature for respective micrometre samples. 相似文献
266.
An investigation into the limiting oxygen concentration (LOC) of fifteen combustible dusts and methane, ethanol and isopropanol hybrid mixtures in the standard 20 L explosion chamber was performed. Three ignition energies (10 J, 2 kJ and 10 kJ) were used. The results show that a 10 J electrical spark ignition leads to significantly higher limiting oxygen concentration values than either 2 kJ or 10 kJ pyrotechnic igniters. This could be due to the “overdriving” effect of the chemical igniters, which produce a hot flame that virtually covers the entire explosion chamber during combustion. With respect to hybrid mixture investigation, the 20 L sphere was modified to allow the input of methane gas and flammable solvents. The limiting oxygen concentrations of the hybrid mixtures were found to be considerably lower than those of dust air mixtures when the relatively weaker spark igniter was used. There was no significant change in limiting oxygen concentration when the higher energy chemical igniters were used. 相似文献
267.
In powder handling and processing industry, location of dust emission can vary, with the suspended dust concentration assessment requiring installation of an immovable or wired equipment. For increased dust sensing, not limited by location within the facility, a portable suspended dust concentration measuring system is needed. In this study, a new method of sensing suspended dust concentration under daylight environment using the change in light extinction coefficient was developed. The method involves capturing images of the suspended dust cloud and then analyzing the light extinction coefficient. This method mitigated the environmental light scattering and absorption and eliminated the noise from the images obtained through a camera by calibration between two targets. Cornstarch, corn dust, and sawdust were used as test materials in this study. The light extinction coefficient (ε) was found to correlate with the suspended dust concentration, and the ε values depended on the dust properties. Mass extinction coefficient (K) was obtained for cornstarch, saw dust and corn dust, from known suspended dust concentrations using image analysis. The mass extinction coefficient of the three sample materials tested in this study were in the range of 0.03–0.04. This method of using light extinction coefficient can be used for real-time sensing of suspended dust concentration in both open and confined spaces. 相似文献
268.
A series of dust explosion were conducted to compare the flame structure between nano and micron aluminium dusts. Two-color pyrometer technique is applied to have qualitative observation of flame development. Measurement of temperature indicates that explosion in micron aluminium dust clouds start in a single spot at 3000 K, in contrast, explosion in nano aluminium dust clouds start when hot powder accumulated to a certain amount at lower temperature of 2600 K. For micron aluminium dust clouds, flame at leading edge has the highest temperature and propagates in all directions. On the other hand, flame in nano aluminium dust clouds propagate only upward with the hottest part left behind at the downside. As flame propagates, the temperature at top edge gradually decreases from 2600 K to finally 2000 K, but temperature at bottom edge maintains in 3000 K with no significant displacement. The unevenness of flame structure is considered as the consequence of different particle densities, which suggests that the reaction of nano aluminium particles stays in molten state, meanwhile, the high surface area also leads to unignorable heat loss. 相似文献
269.
Ivan Iarossi Paul R. Amyotte Faisal I. Khan Luca Marmo Ashok G. Dastidar Rolf K. Eckhoff 《Journal of Loss Prevention in the Process Industries》2013,26(6):1627-1633
The current research is aimed at investigating the explosion behavior of hazardous materials in relation to aspects of particulate size. The materials of study are flocculent (fibrous) polyamide 6.6 (nylon) and polyester (polyethylene terephthalate). These materials may be termed nontraditional dusts due to their cylindrical shape which necessitates consideration of both particle diameter and length. The experimental work undertaken is divided into two main parts. The first deals with the determination of deflagration parameters for polyamide 6.6 (dtex 3.3) for different lengths: 0.3 mm, 0.5 mm, 0.75 mm, 0.9 mm and 1 mm; the second involves a study of the deflagration behavior of polyester and polyamide 6.6 samples, each having a length of 0.5 mm and two different values of dtex, namely 1.7 and 3.3. (Dtex or decitex is a unit of measure for the linear density of fibers. It is equivalent to the mass in grams per 10,000 m of a single filament, and can be converted to a particle diameter.) The explosibility parameters investigated for both flocculent materials include maximum explosion pressure (Pmax), size-normalized maximum rate of pressure rise (KSt), minimum explosible concentration (MEC), minimum ignition energy (MIE) and minimum ignition temperature (MIT). ASTM protocols were followed using standard dust explosibility test equipment (Siwek 20-L explosion chamber, MIKE 3 apparatus and BAM oven). Both qualitative and quantitative analyses were undertaken as indicated by the following examples. Qualitative observation of the post-explosion residue for polyamide 6.6 indicated a complex interwoven structure, whereas the polyester residue showed a shiny, melt-type appearance. Quantitatively, the highest values of Pmax and KSt were obtained at the shortest length and finest dtex for a given material. For a given length, polyester displayed a greater difference in Pmax and KSt at different values of dtex than polyamide 6.6. Long ignition delay times were observed in the BAM oven (MIT measurements) for polyester, and video framing of explosions in the MIKE 3 apparatus (MIE measurements) enabled observation of secondary ignitions caused by flame propagation after the initial ignition occurring at the spark electrodes. 相似文献
270.
Accurate determination of explosion severity parameters (pmax, (dp/dt)max, and KSt) is essential for dust explosion assessment, identification of mitigation strategy, and design of mitigation measure of proper capacity. The explosion severity parameters are determined according to standard methodology however variety of dust handled and operation circumstances may create practical challenge on the optimal test method and subsequent data interpretation. Two methods are presented: a statistical method, which considers all test results in determination of explosion severity parameters and a method that corrects the results for differences of turbulence intensity. The statistical method also calculates experimental error (uncertainty) that characterises the experimental spread, allows comparison to other dust samples and may define quality determination threshold. The correction method allows to reduce discrepancies between results from 1 m3 vessel and 20-l sphere caused by difference in the turbulence intensity level. Additionally new experimental test method for difficult to inject samples together with its analysis is described. Such method is a versatile tool for explosion interpretation in test cases where different dispersion nozzle is used (various turbulence level in the test chamber) because of either specific test requirements or being “difficult dust sample”. 相似文献