Air sampling

Because processes such as diffusion and partitioning are fundamentally the same in water and air, equations that describe uptake from air can be obtained by replacing the subscripts in equations for water with those appropriate for air 

No published values of SPMD-air partition coefficients (A sa) exist. These values therefore have to be calculated from published values of and Henry s law constants H) using 

No large variation in sampling rates is observed among the different studies, despite differences in exposure conditions, such as wind speeds, temperature, and SPMD mounting layout. It should be noted, however, that the effect of temperature is partially accounted for by our use of temperature-corrected log A oa values. An example of the application of Eq. 3.68 for calculating atmospheric concentrations is given in Box 3.3. 

3 Example of the Calculation of Atmospheric Concentrations of Vapor-Phase Compounds Using Eq. 3.68 

The temperature dependence of yields additional information on the issue of whether the membrane or the ABL controls the uptake rates. In the case of membrane-controlled uptake, the sampling rates are given by 

Most of the sampling carried out In the atmosphere is intended for the determination of pollutants or their effects in localized industrial areas or areas devoted to global environmental studies. Only ocassionally (e.g. measurements of boron [19] or nitrogen oxides in air [20]) are these studies aimed at the Identification of the geochemical cycle of some species in the atmosphere. 

Systems for sampling of airborne pollutants usually consists of three parts (a) a means of collecting the air sample (b) a device to trap the pollutant and (c) a means of measuring the amount of air sampled. The sampling methods frequently used for this purpose are sedimentation [21,22], centrifugation [23], impaction, filtration and thermal or electrostatic precipitation [24,25], the commonest of which are filtration, impaction and electrostatic precipitation. The size of the collected particles depends on the particular method used. 

Filtration Is the sampling method most frequently used in industrial hygiene work (personal monitors) on account of its operational simplicity. A filter assembly typically consists of a sampling head and a filter (passive atmospheric samplers) or a sampling head, filter and pump (active samplers), all of which are constructed In a material introducing no contamination In the samples. The different types of filters (depth, membrane) and materials (glass fibre, quartz, cellulose esters, PFTE, sliver) used can be readily adapted to the unknown analyte. 

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. 

Electrostatic precipitation Is specific for suspended particles and is thus widely used In this type of sampling [26,27]. 

Metal concentrations in indoor reported in units of ig m or ng m (Table 11.3), and are generally orders of 

Representative German population (600 households with children aged 6-14 years) Geometric mean 5.4 0.39 0.016 0.008 

Smelter town in eastern Germany (454 households with children aged 4-15 years) Geometric mean 8.9 1.14 0.024 0.023 

Residential monitoring (UK) Indoor range (Geo. mean) n — 607 Outdoor range (Geo. mean) n = 605 

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The use of air-bome ultrasound for the excitation and reception of surface or bulk waves introduces a number of problems. The acoustic impedance mismatch which exists at the transducer/air and the air/sample interfaces is the dominant factor to be overcome in this system. Typical values for these three media are about 35 MRayls for a piezo-ceramic (PZT) element and 45 MRayls for steel, compared with just 0.0004 MRayls for air. The transmission coefficient T for energy from a medium 1 into a medium 2 is given by... 

This corresponds to the physician s stethoscope case mentioned above, and has been realized [208] by bringing one leg of a resonatmg 33 kHz quartz tiinmg fork close to the surface of a sample, which is being rastered in the x-y plane. As the fork-leg nears the sample, the fork s resonant frequency and therefore its amplitude is changed by interaction with the surface. Since the behaviour of the system appears to be dependent on the gas pressure, it may be assumed that the coupling is due to hydrodynamic mteractions within the fork-air-sample gap. Since the fork tip-sample distance is approximately 200 pm -1.120), tire teclmique is sensitive to the near-field component of the scattered acoustic signal. 1 pm lateral and 10 mn vertical resolutions have been obtained by the SNAM. 

After adding p-rosaniline and formaldehyde, the colored solution was diluted to 25 ml in a volumetric flask. The absorbance was measured at 569 nm in a 1-cm cell, yielding a value of 0.485. A standard sample was prepared by substituting a 1.00-mL sample of a standard solution containing the equivalent of 15.00 ppm SO2 for the air sample. The absorbance of the standard was found to be 0.181. Report the concentration of SO2 in the air in parts per million. The density of air maybe taken as 1.18 g/L. 

HPEC Determinations of Acrylamide in Water and Air Samples, AnalyticalMethod PAA 58,61 in Forms 260-951-88, Chemicals and Metals Department, The Dow Chemical Company, Midland, Mich., 1981. 

J. P. Lodge, ed.. Methods of Air Sampling and Analysis, Lewis PubUshers, Chelsea, Mich., 1989, 763 pp. 

American Conference of Governmental Industrial HygiemsX.s, Advances in Air Sampling ACGIH, Cincinnati, Ohio, 1988. 

However, if air sampling estabHshes that the lead exposure concentration is excessive, engineering controls (such as improved ventilation), adrninistrative controls (such as job rotation), and work practices (such as improved personal hygiene of workers) have to be appHed to comply with the permissible exposure limit (PEL) of the OSHA standard. 

Sulfur dioxide concentrations as low as 40 mg/m in air have been determined bypassing air samples through an aqueous solution of tetrachloromercurate, which converts SO2 to the dichlorosulfitomercurate complex. Oxidation of the complex by potassium permanganate is chemiluminescent and the intensity, as measured by a photomultipHer, is proportional to sulfur dioxide concentration (312). 

The contrast for specimen detail in the field of view is gready enhanced by darkfield illumination (10). The degree of contrast and sensitivity of detection of smaH-object details depend on the relative indices of the specimen and the mounting Hquid and on the intensity of the illumination. Darkfield illumination is not, however, a satisfactory solution for biologists who need direct transmitted light in order to observe specimens, especially stained specimens. It is, however, very usefiil in detecting asbestos fibrils that often exist in door tiles or water and air samples as 20-nm fibers (10 times finer than the resolution of an asbestos analyst s usual microscope) (11). Darkfield illumination yields an uimatural appearance and difficulties in interpretation hence, a need for better contrast methods stiU exists. 

Health and Safety. Remover formulas that are nonflammable may be used in any area that provides adequate ventilation. Most manufacturers recommend a use environment of 50—100 parts per million (ppm) time weighted average (TWA). The environment can be monitored with passive detection badges or by active air sampling and charcoal absorption tube analysis. The vapor of methylene chloride produces hydrogen chloride and phosgene gas when burned. Methylene chloride-type removers should not be used in the presence of an open flame or other heat sources such as kerosene heaters (8). 

Health and Safety. Petroleum and oxygenate formulas are either flammable or combustible. Flammables must be used in facUities that meet requirements for ha2ardous locations. Soak tanks and other equipment used in the removing process must meet Occupational Safety and Health Administration (OSHA) standards for use with flammable Hquids. Adequate ventilation that meets the exposure level for the major ingredient must be attained. The work environment can be monitored by active air sampling and analysis of charcoal tubes. 

MDA Content of Air Samples, SRI International, Menlo Paik, Calif., 1986. 

A method suitable for analysis of sulfur dioxide in ambient air and sensitive to 0.003—5 ppm involves aspirating a measured air sample through a solution of potassium or sodium tetrachloromercurate, with the resultant formation of a dichlorosulfitomercurate. Ethylenediaminetetraacetic acid (EDTA) disodium salt is added to this solution to complex heavy metals which can interfere by oxidation of the sulfur dioxide. The sample is also treated with 0.6 wt % sulfamic acid to destroy any nitrite anions. Then the sample is treated with formaldehyde and specially purified acid-bleached rosaniline containing phosphoric acid to control pH. This reacts with the dichlorosulfitomercurate to form an intensely colored rosaniline—methanesulfonic acid. The pH of the solution is adjusted to 1.6 0.1 with phosphoric acid, and the absorbance is read spectrophotometricaHy at 548 nm (273). 

In the United States, the largest concentration of atmospheric vanadium occurs over Eastern seaboard cities where residual fuels of high vanadium content from Venezuela are burned ia utility boilers. Coal ash ia the atmosphere also coataias vanadium (36). Ambient air samples from New York and Boston contain as much as 600—1300 ng V/m, whereas air samples from Los Angeles and Honolulu contained 1—12 ng V/m. Adverse pubHc health effects attributable to vanadium ia the ambieat air have aot beea deteroiiaed. lacreased emphasis by iadustry oa controlling all plant emissions may have resulted ia more internal reclamation and recycle of vanadium catalysts. An apparent drop ia consumption of vanadium chemicals ia the United States since 1974 may be attributed, in part, to such reclamation activities. 

Rapid, simple, quaUtative methods suitable for determining the presence of benzene in the workplace or surroundings have been utilized since the 1930s. Many early tests offered methods for detection of aromatics but were not specific for benzene. A straightforward test allowing selective detection of benzene involves nitration of a sample to y -dinitrobenzene and reaction of the resultant ether extract with an ethanoHc solution of sodium hydroxide and methyl ethyl ketone (2-butanone), followed by the addition of acetic acid to eliminate interferences from toluene and xylenes. Benzene imparts a persistent red color to the solution (87). The method is claimed to be sensitive to concentrations as low as 0.27 ppm benzene from 10 mL air samples. 

Determination of benzene in air samples has been achieved by bubbling contaminated air through various solvents, followed by uv or in analysis of the solution (90). Methods for identifying benzene in soil, water, and biological media are further described in references 84 and 85. 

Operations capable of generating airborne beryUium particulate, such as melting, machining, welding, grinding, etc, are effectively controUed by local exhaust ventilation or other control measures. To assure a safe environment and measure compliance with the OSHA standards, employee exposures should be periodicaUy measured by prescribed air sampling and analytical methods. 

PCBs have been identified in ambient air samples from diverse locations (15—17,18). In one study of the atmospheric levels of several halogenated... 

Polymers. Studies to determine possible exposure of workers to residual epichl orohydrin and ethylene oxide monomers in the polymers have been done. Tests of warehouse air where Hydrin H and Hydrin C are stored showed epichl orohydrin levels below 0.5 ppm. Air samples taken above laboratory mixing equipment (Banbury mixer and 6" x 12" mill) when compounds of Hydrin H or C were mixed gave epichl orohydrin levels below detectable limits, and ethylene oxide levels less than 0.2 ppm, well below permissible exposure limits (46). A subacute vapor inhalation toxicity study in which animals were exposed to emission products from compounded Parel 58 suggests that no significant health effects would be expected in workers periodically exposed to these vapors (47). 

How does the range of concentrations of air pollutants of concern to the industrial hygienist differ from that of concern to the air pollution specialist To what extent are air sampling and analytical methods in factories and in the ambient air the same or different ... 

Hydrocarbon Compounds Identified in Ambient Air Samples from St. Petersburg, Florida... 

Regardless of the configuration or the specific material sampled, several characteristics are important for all ambient air sampling systems. These are collection efficiency, sample stability, recovery, minimal interference, and an understanding of the mechanism of collection. Ideally, the first three would be 100% and there would be no interference or change in the material when collected. 

Hering, S. V., "Air Sampling Instruments for Evaluation of Air Contaminants." ACGIH, Cincinnati, OH, 1989... 

The methods that have been discussed require specially designed instruments. Laboratories without such instruments can measure these gases using general-purpose chemical analytical equipment. A compendium of methods for these laboratories is the "Manual on Methods of Air Sampling and Analysis"published by the American Public Health Association. (10). 

Analytical methods available to labbratories with only general-purpose analytical equipment may be found in the "Methods of Air Sampling and Analysis" cited at the end of the previous section. 

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