5.Nephelometer
What a Nephelometer Is:
The TSI-3563 is a high-sensitivity device capable of detecting the scattering properties of aerosol particles. It designed for long-term monitoring of visual range and air quality in both ground-based and airborne uses, specifically for studies of radiative forcing of the Earth's climate by aerosol particles and studies of atmospheric visual air quality. The nephelometer detects by measuring the amount of light, or photons, scattered by the aerosol and then subtracts light scattered by the walls of the measurement chamber, light scattered by the atmospheric gasses present (Rayleigh scattering), and the electronic noise inherent to the detector system. It may also be used after a pretreatment step, such as heating, humidification or segregation by size.
The light scattering coefficient is a highly variable aerosol property. This instrument measures the angular integral of light scattering that yields the quantity called the scattering coefficient, used in the Beer-Lambert Law to calculate total light extinction.
System Functions
The instrument works in the following manner. A small blower continuously draws in an aerosol sample (eg. atmospheric air that has been reduced to 40% RH by heating before inlet.) The sample is illuminated by a halogen lamp directed through an optical light pipe. The sample volume is viewed by three photomultiplier tubes (PMT) through a set of aperture plates (see cut-away diagram below.) Aerosol scattering is viewed against a backdrop of a very efficient light trap, where all internal surfaces are coated to give a very light low scatter. Dichroic filters split and redirect the scattered light into three bandpass filters, red, green and blue.
A constantly rotating disc, the reference chopper, interrupts the beam going to the PMT tubes. The chopper has three separate areas to provide three types of signal detection. The first area gives a measure of the light scattering signal passing through a notch in the chopper. The second area blocks all light and gives a measurement of the PMT dark current, and is subtracted from the first signal. The third is translucent and illuminated by the lamp, providing a measure of the light illumination intensity, used to compensate for light source variation.
In backscatted mode, a backscatter shutter rotates under the lamp to block sample illumination in the 7 to 90° range. When light is blocked, only light scatered in the backward direction is detected by the PMT
6. TRIBO ELECTRICITY (Nothing about Devices):
The triboelectric effect (also known as 'triboelectric charging') is a type of contact electrification in which certain materials become electrically charged after they come into contact with another different material and are then separated (such as through rubbing). The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties.
Thus, it is not very predictable, and only broad generalizations can be made. Amber, for example, can acquire an electric charge by contact and separation (or friction) with a material like wool. This property, first recorded by Thales of Miletus, suggested the word "electricity", from the Greek word for amber, ēlektron. Other examples of materials that can acquire a significant charge when rubbed together include glass rubbed with silk, and hard rubber rubbed with fur.
The Wimshurst machine creates large sparks by development of frictional charge
Although the word comes from the Greek for "rubbing", tribos, the two materials only need to come into contact and then separate for electrons to be exchanged. After coming into contact, a chemical bond is formed between some parts of the two surfaces, called adhesion, and charges move from one material to the other to equalize their electrochemical potential. This is what creates the net charge imbalance between the objects. When separated, some of the bonded atoms have a tendency to keep extra electrons, and some a tendency to give them away, though the imbalance will be partially destroyed by tunneling or electrical breakdown (usually corona discharge). In addition, some materials may exchange ions of differing mobility, or exchange charged fragments of larger molecules.
The triboelectric effect is only related to friction because they both involve adhesion. However, the effect is greatly enhanced by rubbing the materials together, as they touch and separate many times. For surfaces with differing geometry, rubbing may also lead to heating of protrusions, causing pyroelectric charge separation which may add to the existing contact electrification, or which may oppose the existing polarity. Surface nano-effects are not well understood, and the atomic force microscope has made sudden progress possible in this field of physics.
Because the surface of the material is now electrically charged, either negatively or positively, any contact with an uncharged conductive object or with an object having substantially different charge may cause an electrical discharge of the built-up static electricity; a spark. A person simply walking across a carpet may build up a charge of many thousands of volts, enough to cause a spark one centimeter long or more. Dry conditions inhibit electrical discharge by decreasing the conductivity of the air, as is common indoors in very cold weather. Simply removing a nylon shirt or corset can also create sparks, and car travel can lead to a build-up of charge on the metal car body (which acts as a Faraday cage). When the driver alights, sparks jump from frame to driver as he makes contact with the ground.
This type of discharge is often harmless because the energy ((V2 * C)/2) of the spark is very small, being typically several tens of micro joules in cold dry weather, and much less than that in damp conditions. However, such sparks can ignite methane-air mixtures, and is a danger when leaks of natural gas occur in domestic buildings, for example. Gas leaks are a serious hazard and can cause physical damage and death.
Aircraft flying in weather will develop a static charge from air friction on the airframe. The static can be discharged with static dischargers or static wicks.
The effect is of considerable industrial importance in terms of both safety and potential damage to manufactured goods. The spark produced is fully able to ignite flammable vapours, for example, petrol, ether fumes as well as methane gas.
Means have to be found to discharge carts which may carry such liquids in hospitals. Even where only a small charge is produced, this can result in dust particles being attracted to the rubbed surface. In the case of textile manufacture this can lead to a permanent grimy mark where the cloth has been charged. Some electronic devices, most notably CMOS integrated circuits and MOSFET transistors, can be accidentally destroyed by high-voltage static discharge. Such components are usually stored in a conductive foam for protection. Grounding self by touching the workbench, others, or using a special bracelet or anklet is standard practice while handling unconnected integrated circuits. Another way of dissipating charge is by using conducting materials such as carbon black loaded rubber mats in operating theatres.
7. IMPACTION DEVICES:
A slit impaction sampling device is for collecting airborne contaminants for subsequent analysis, includes a base with a microscope slide disposed thereon. The microscopic slide has an adhesive media located thereon to assist in adhering airborne particles on the microscopic slide. The base has a top cap secured thereto. The top cap has an inlet opening formed therethrough. The inlet opening has an outer venturi section and an inner laminar section that directs the air flow through the inlet opening into contact with the adhesive media such that the airborne particles form an impaction trace thereon. The air then flows around the microscope slide into an outlet passage and to a vacuum source.
An airborne particle impaction sampler, comprising: a base; a microscope slide disposed on said base; an adhesive media located on said microscope slide to assist in adhering airborne particles on said microscope slide; a top cap secured to said base, said top cap having an inlet opening formed therethrough, said inlet opening being configured as a slit, the upper surface of the top cap defining the inlet opening including opposed substantially parallel side portions and opposed outwardly radiused arcuate end portions extending between and interconnecting the ends of the side portions; and an inlet passageway extending from the inlet opening, the top cap defining a first portion and a second portion of the inlet passageway, the first portion of the inlet passageway including opposed planar side walls converging inwardly from a top edge integral with the side portions of the inlet opening to coplanar bottom edges, and outwardly radiused arcuate end walls converging inwardly from a top edge integral with the end portions of the inlet opening to bottom edges coplanar with the bottom edges of the side walls, the end walls extending between and interconnecting the side walls, and the second portion of the inlet passageway including substantially parallel side walls extending from a top edge integral with the bottom edges of the side walls of the first portion of the inlet passageway to coplanar bottom edges, and opposed outwardly radiused arcuate end walls extending from a top edge integral with the bottom edges of the end walls of the first portion of the inlet passageway to bottom edges coplanar with the bottom edges of the parallel side walls, the opposed end walls of the second portion of the inlet passageway extending between and interconnecting the parallel side walls, and the bottom edges of the side walls and the end walls of the second portion of the inlet passageway defining an outlet opening adjacent the microscope slide such that air entering the sampler impacts said adhesive media.
A method of gathering airborne particles into an impaction sampler, the airborne particles gathering method comprising: providing a housing having an inlet opening formed therethrough, the inlet opening being configured as a slit, the upper surface of the housing defining the inlet opening including opposed substantially parallel side portions and opposed outwardly radiused arcuate end portions extending between and interconnecting the ends of the side portions, and an inlet passageway extending from the inlet opening, the housing defining a first portion and a second portion of the inlet passageway, the first portion of the inlet passageway including opposed planar side walls converging inwardly from a top edge integral with the side portions of the inlet opening to coplanar bottom edges, and outwardly radiused arcuate end walls converging inwardly from a top edge integral with the end portions of the inlet opening to bottom edges coplanar with the bottom edges of the side walls, the end walls extending between and interconnecting the side walls, and the second portion of the inlet passageway including substantially parallel side walls extending from a top edge integral with the bottom edges of the side walls of the first portion of the inlet passageway to coplanar bottom edges, and opposed outwardly radiused arcuate end walls extending from a top edge integral with the bottom edges of the end walls of the first portion of the inlet passageway to bottom edges coplanar with the bottom edges of the parallel side walls, the opposed end walls of the second portion of the inlet passageway extending between and interconnecting the parallel side walls, and the bottom edges of the side walls and the end walls of the second portion of the inlet passageway defining an outlet opening; locating a microscope slide in said housing adjacent the outlet opening, said microscope slide having an adhesive media applied thereon; drawing air through the inlet opening formed in said housing and into the inlet passageway; accelerating said drawn air in first portion of said inlet passageway after it has passed through said inlet opening; and passing said accelerated air from said first portion of said inlet passageway to said second portion of said inlet passageway, such that the drawn air exits the outlet opening and impacts said adhesive media.
An impaction air sampler, comprising: a housing having an upper portion and a lower portion; a recess formed in said lower portion of said housing; a slide located within said recess; an inlet passageway being formed in said upper portion of said housing and opening into the housing adjacent said slide; said lower portion of said housing having a bore with greater depth than the recess, the bore sized to allow air to flow around said slide, the longest planar dimension of the bore at the inner surface of the lower portion of said housing being less than the longest dimension of the slide, wherein the lower portion of said housing defines opposed slots extending radially outwardly of the bore forming the recess for receiving the slide; and said housing having an outlet passage in communication with said bore at one end and a remote vacuum source located exterior to said housing at another end.
Obtaining accurate samples of airborne particles such as mold spores, pollen, skin fragments, insect parts, various fibers, and other aeroallergens is necessary or desirable for a number of different purposes, including reliable contamination studies. For example, environmental professionals need accurate samples to determine the presence and quality of deleterious such as asbestos fibers in the air. Furthermore, aero-biologists and allergists need accurate samples to identify and quantify airborne pollen and mold spore concentrations for patient diagnosis. Moreover, epidemiologists require accurate samples to determine the presence of particles carrying bacteria, such as that responsible for Legionnaire's Disease, in air-conditioning systems and the like.
Various sampling methods and techniques are well known for use in providing particle analysis in a variety of different areas and applications. One such sampling method is filter sampling, which is well known for use in particle and fiber analysis. With filter sampling methods, air is drawn through a microporous filter as is known and the filter can then be examined under a microscope to determine the type and concentration of particles trapped on the filter. While effective for some purposes, filter sampling is time consuming and provides only limited reliability. For example, large particles such as pollen, often do not remain attached to the filter, separating therefrom during transportation and handling.
Slit or impaction samplers, which direct air at relatively high velocity through a narrow rectangular slit against a tacky material have a number of advantages over filter sampling. With slit air samplers, samples sufficient for analysis can be obtained in minutes rather than hours, the area to be examined is much smaller than the areas provided with filters, and the tacky nature of the material used to collect the sample will retain large particles better than filters. However, the configuration of these designs does not always ensure the desired accurate particle accumulation. Moreover, these samplers typically can only be used in an upright or fixed position and cannot be easily used in confined or restricted spaces because of their relatively large size.
One current sampler, which is described in U.S. Pat. No. 5,693,895, attempts to solve some of these problems by providing a smaller system with a removable sampling cell that minimizes handling of the slide at the sampling site. This sampler, however, requires the usage of a new sampling cell for each sampling run, thereby making it relatively expensive. Additionally, the disclosed sampler suffers from some disadvantages in airflow into the sampler that can lead to an incomplete gathering of air particles and therefore affect any conclusions drawn from an analysis thereof.
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