Sampling atmospheric

Ion-selective electrodes can also become sensors (qv) for gases such as carbon dioxide (qv), ammonia (qv), and hydrogen sulfide by isolating the gas in buffered solutions protected from the sample atmosphere by gas-permeable membranes. Typically, pH glass electrodes are used, but electrodes selective to carbonate or sulfide may be more selective. 

ASTM. 1987a. Standard practice for sampling atmospheres to collect organic compound vapors (activated charcoal tube adsorption method) - method D 3686-84. In 1987 annual book of ASTM standards. Vol. 11.03. Atmospheric analysis occupational health and safety. Philadelphia, PA American Society for Testing and Materials, 326-336. 

Delumyea, R.G. Chu, L-C. Macias, E.S., Determination of Elemental Carbon Component of Soot in Ambient Aerosol Samples, Atmospheric Environment. 1980, 14, 647-652. 

The sampling atmosphere is an important factor. The sampling atmosphere may be an inert gas, or reactive gas or vacuum. When a gas is used, the atmosphere can either be flowing through the measurement chamber or static (i.e. nonflowing). If the atmosphere is static, the decomposition products may remain in the area of the sample and cause secondary reactions to occur, which are not necessarily related to the heating process. 

The sampling operation involves collection of an aerosol sample that is representative of the particle size distribution and concentration of the sampled atmosphere. The efficiency of particle transport and collection operations are dependent on the particle size, sampling velocity, the geometry of the sampling apparatus and the properties of the collection medium. In the present work, a 37 mm diameter membrane filter (0.3 ym pore size) is the primary collection medium under evaluation. The filter is housed in a standard filter cassette and effects of filter-holder inlet geometry are also being investigated. 

Collection. Formic acid in diluted (1 10) diesel exhaust or mine air was collected by drawing the sample atmosphere through two fritted bubblers (10) in series, each containing 15 mL of 10 3 M Na2C03. A flow rate of 1.0 liter per minute and collection time of 60 minutes for diluted diesel exhaust or 240 minutes for mine air was used. A 37 mm glass fiber filter (Gelman Type A/E) was placed before the bubblers to remove particulates. 

In order to improve our knowledge about the marine aerosol and its formation we established a land-based aerosol sampling station on the western coast of Terceira island (Azores). Here we present the first measurements of a project of sampling atmospheric particulate matter which started in Spring of 1999 and will be extended for one year. 

Martin, N.A., Marlow, D.J., Henderson, M.H., Goody, B.A. and Quincey, P.G. (2003) Studies using the sorbent Carbopack X for measuring environmental benzene with Perkin-Elmer-type pumped and diffusive samples. Atmospheric Environment, 37, 871-9. 

Fan, X., Brook, J.R. and Mabury, S.A. (2003) Sampling atmospheric carbonaceous aerosols using an integrated organic gas and particle sampler. Environmental Science and Technology, 37, 3145-51. 

Atmosphere The nature of the atmosphere surrounding the sample is important in relation to the transfer of heat and the chemistry of the sample reaction. Common sample atmospheres are shown in Table 36.1. In addition, the flow rate of the gas is important a static system will not remove reaction products from the sample. 

The method of Fan and Dasgupta (1994) relics on tlie reaction of formaldehyde with 1,3-cyclohexane-dione in acidified ammonium acetate to form the fluorescent dihydropyridine derivative in a flow injection analysis system. Formaldehyde trapped in water can be reacted with pararosaniline and sodium sulfite under mild conditions (neutral pH, room temperature equilibration) to produce a colored product that is measured at 570 nm (Petreas et al. 1986). The presence of bisulfite is an interference in this reaction so the method cannot be used to sample atmospheres that contain sulfur dioxide. In addition, the method is reported to suffer from interferences resulting from the presence of other aldehydes and phenol (Hoogenboom et al. 1987). The indirect method of Hoogenboom et al. (1987) relies on the reaction of excess bisulfite in an aqueous solution of formaldehyde with 5,5 -dithiobis(2-nitrobenzoic acid) to form a colored product, the absorbance of which is measured at 412 nm. The method reported by Naruse et al. (1995) relies on the formation of a colored product obtained by reacting the aqueous formaldehyde with acetylacetone and ammonium acetate in acetic acid. Absorbance is measured at 414 nm. 

Identification of sample atmosphere, flow rate, and purity... 

Spicer, C. W. and Schumacher, P. M., 1977 Interferences in sampling atmospheric particulate nitrate. Atmospheric Environment IL 873-876. 

Barrall and Rogers (70) described a constant-pressure device mol a sealed-tube type sample holder) which is illustrated in Figure 6.20. Total cell volume was about 0.8 ml a glass capillary tube provides a reservoir for the gases released during a reaction and prevents significant dilution of the sample atmosphere with air or the loss of gas. The small mercury seal provides for sample atmosphere expansion and maintains an essentially constant pressure in the cell. 

An identification of the sample atmosphere by pressure, composition, and purity, and by whether the atmosphere is self-generated or dynamic through or over the sample. The flow rate, total volume, construction, and temperature of the system between the sample and detector should be given, together with an estimate of the time delay within this system. 

Generally, in the previously described heated sample holders, few attempts were made to control the atmosphere surrounding the sample as it was heated. A cover plate of Pyrex glass or quartz was employed but its main purpose was to prevent the sample from accidentally falling into the integrating sphere of the spectroreflectometer. In order to control the sample atmosphere, the sample holder shown in Figure 9.3 was constructed by Wendlandt and Dosch (16). 

A pump is usually employed to transport the air sample along the sampling device, where the air stream Impinges on a solid surface (Impactors or adsorption tubes) or a solution (implngers) where the particles or gases settle. The solid use for impaction or adsorption and the absorbing solution are suited to the type of compound to be determined and to the nature of the sampled atmosphere. 

The method(s) for analyzing the exposure atmosphere. Sampling atmospheres from the exposure system can be conducted continuously or sequentially and periodically for measurement of test material concentration, and... 

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