Filtration, sampling aerosols

The simplest approach to sampling aerosols is to use filtration or an inertial device that traps all the airborne material. This would be useful for determining the total amount... 

As mentioned briefly in the first chapter when we considered the filtration of aerosol samples, a recent innovation in the construction of sieves using a matrix of fiberoptic elements has been described for the construction of sieves made of glass. Information on these sieves are available from Collimated Holes Incorporated [29]. 

For aerosols of nonvolatile pesticides (e.g., paraquat) and aerosols containing pesticides, sampling methods consisting of filtration and employing inertial samplers... 

Particles can be solid or liquid in air (gas) and the mixture consitutes an aerosol. Their typical dimensions are >0.001 Xm and they can be sampled by filtration. 

Collection on porous filter media is perhaps the most efficient means of particle removal. Aerosol filtration is an effective means of air purification, while at the same time it has been widely used for sampling airborne material for mass and chemical composition determination. A wide variety of filter media is available, ranging from fibrous mats of relatively inert material to porous membranes. Fibrous mats and model filter arrays appear microscopically as stacks of overlaid cylinders, where the cylinders may be smooth or rough. In contrast, the membrane media are plastic films with microscopic holes of nearly uniform size nuclepore filters, for example, are produced of sheets of polyester, and the holes are introduced by neutron bombardment. 

Filtration is a suitable method for the collection of aerosols for microscopy, as mentioned previously. Particles may also be collected using inertial devices and may be examined by microscopy [73]. A third method that has not been mentioned is electrostatic precipitation, or sampling. 

The effectiveness of this approach was demonstrated by measuring the cumulative fluorescence of 1-micron-size blue fluorescent microspheres versus cumulative volume withdrawn from our WEP collector after capture from an aerosol suspension of about 140 particles/ml drawn from a test chamber over a 5-minute period at a sampling rate of 500 liters/minute. As the liquid was being withdrawn from the WEP collector, it was filtered at a rate of 1 ml/second and the filter back-flushed with small portions of filtrate at 1-minute intervals. The relative cumulative concentration of captured particles in the first back-flushed 1-ml fraction was around 56 as compared with a value of 1.4 in the first 60-ml filtered fraction, which constitutes a liquid-to-liquid concentration enhancement by a factor of 40 and an air-to-liquid concentration factor olYl.25 x 10. ... 

High-efficiency filtration is the most common method of collecting particulate mailer for the determination of chemical composition. Chemical analysis of filter. samples provides information on the composition of the aerosol averaged over all particle sizes and over the time interval of sampling. For a constant gas-sampling rate, the mass concentration of species i averaged over particle size and time is related to the size compo.sition probability density function as follows ... 

Sample preparation Solutions, capsules. Dilute solutions and capsule contents with water so as to achieve a cromolyn concentration of 40 jxg/mL, iiyect a 20 pL aliquot. Aerosols. Direct aerosol into a flask, dissolve collected sample in water so as to achieve a cromolyn concentration of 40 (Ag/mL, filter (0.45 p.m), inject a 20 jjiL aliquot of the filtrate... 

Several sampling methods in eommon use rely upon air filtration to remove bioaerosols from a sampled air volume. Generally the aerosols are removed by a combination of impaction on the filter surface as well as interception, electrostatic attraction, and diffusion deposition. After sampling, filters are agitated in a solution to re-entrain the microbes and this solution is then serially diluted and plated onto appropriate culture media. 

In the analysis of a marine aerosol, the flrst step is to divide it into a water-soluble fraction which we call salt and an insoluble fraction referred to as dust. This is achieved by washing the collecting nylon sail or filter with distilled water (12). The dust is removed from the suspension by centrifugation and filtration. It is dried at 110°C and weighed. The salt is either isolated from an aliquot of the supemate by freeze drying, or the dissolved ions of interest are determined directly. The amount of salt in each sample is determined by weighing or by summing the major constituents. 

The exhaust air from a radio-chemical laboratory should be filtered to extract dust. In general, however, no additional exhaust air treatment is necessary in a water laboratory measuring radioactivity in water samples. The exhaust air is monitored for radio-active aerosols by filtration of a specific quantity of air via membrane filters, and by measuring the deposit on the membrane filter. 

Filtration Air is filtered for collection of aerosols by drawing the air sample through glass fiber, cellulose, sintered glass, or membrane or granular filters. On accumulation of the aerosol the flow through the filter is restricted, and collection is influenced by... 

Kito, A-JVUM. and Colbeck, I. (1999) Filtration and denuder sampling techniques, in Analytical Chemistry of Aerosols (ed. K.R. Spumy), CRC Press, Chapter 4, pp. 103-132. 

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