Chlorides airborne

Airborne salinity refers to the content of gaseous and suspended salt in the atmosphere. It is measmed by the concentration in the air in units of ig/m. Since it is the salt that is deposited on the metal surface that affects the corrosion, it is usually reported in terms of deposition rate in units of mg/mVday. Chloride levels can also be measured in terms of the concentration of the dissolved salt in rain water. 

A number of methods have been employed for determining the contamination of the atmosphere by aerosol transported chlorides, for example, sea salt and road deicing salts. The wet candle method, for 

In reality, the wet candle method gives an indication of the salinity of the atmosphere rather than the contamination of exposed metal surfaces. The technique is considered to measure the total amount of chloride arriving to a vertical surface and its results may not be truly significant for corrosivity estimates. 

In order to understand the chloride deposition rates in a confined spaces, such as ventilated subfloors in a sea coastal area, a special collecting box shown in Fig. 9.25 was used in which the airborne chlorides were collected on horizontal and vertical filter papers positioned at different locations from the box openings (Fig. 9.26). 

The roof protected the surface from direct rain but the filter papers were still exposed to deposition of the airborne chlorides and possibly some rain. Filter papers were removed every month for chemical analysis. A wet candle with its own roof cover was installed on each box (Fig. 9.25) to provide a measure of the level of chlorides outside the boxes. 

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XDl Moderate humidity Concrete surfaces exposed to airborne chlorides. 

Ambler (I960) found that humidity and temperature in the tropics magnify effects (Table 2.6) but reported no apparent direct correlation between corrosion and the presence of these three chemical compounds. Airborne chlorides responsible for increased corrosion in tropical and desert areas were reported by Compton (1947) and Machu (1954). Compton noted that corrosion caused by condensed moisture in some tropical islands is aggravated by chlorides from coral dust. Machu noted a similar effect on zinc in Egypt about 225 km from the sea. The desert sand and dust at this location... 

Airborne salinity can be determined using different methods. In corrosion research the standard method (Wet Candle method) is established in ISO-9225 1992 [33] however, it is not the only method traditionally used. In the case of Cuba it has been widely used the method named as dry plate method, consisting in the employment of a dry cotton fabric of known area exposed under a shed. The amount of chloride deposition on the gauze is determined analytically at the end of the exposure period (two months) and the deposition rate is calculated. 

Bauer et ah, 1986). It is also a significant corrosion product of Fe alloy phases on Antarctic meteorites where its formation is induced by the chloride ions coming from airborne seaspray and/or volcanic activity (Buchwald and Clarke, 1989). In these meteorites, akaganeite is located adjacent to the corroding surface and beneath a layer of goethite/spinel into which it eventually transforms. 

A third factor comes into play in bromine chemistry, which is that atmospheric solutions containing bromide and chloride are most typically formed from seawater. Wave action generates small airborne droplets of seawater, which thus initially contain the elements in the ratios found in seawater. The molar ratio of Br- to Cl- is 1 650. However, despite the relatively small amounts of bromide relative to chloride, it plays a disproportionate role because of its reactivity and because its chemistry is closely intertwined with chloride ion chemistry. Table 8.16, for example, shows some of the interhalogen reactions of bromide and chloride. It can be seen that the chemistry preferentially generates Br2 rather than Cl2. 

Sinclair, J. D., L. A. Psota-Kelty, C. J. Weschler, and H. C. Shields, Deposition of Airborne Sulfate, Nitrate, and Chloride Salts as It Relates to Corrosion of Electronics, J. Electrochem. Soc., 137, 1200-1206 (1990a). 

The California Air Resources Board has prepared risk assessments for a number of toxic airborne compounds and mixtures, designated as toxic air contaminants, TACs (Table 16.15). For example, risk assessments for individual compounds such as benzene, benzo[a]pyrene (see Chapter 10), formaldehyde, and vinyl chloride have been carried out, in addition to complex mixtures such as diesel exhaust (California Air Resources Board, 1997a) and environmental tobacco smoke (California Environmental Protection Agency, 1997). These risk assessment documents form the basis for controls imposed as part of the risk management process (e.g., see Seiber, 1996). 

Recommended Method airborne particles collected on a sorbent cartridge containing polyurethane foam particulates deposited on the filter extracted with methylene chloride extract analyzed by GC-FID or GC/MS recommended air flow 5 L/min sample volume 1000 L. 

Hydrogen chloride is the first chlorine-bearing interstellar molecule to have been detected. Its lowest rotational transition (J = 1 -> 0) at 625.9 GHz has been observed in the Orion Molecular Cloud (OMC-1) in emission with the Kuiper Airborne Observatory, (Blake, Keene, and Phillips, 1985) since atmospheric opacity at this... 

Most often, trip blank contamination originates in the laboratory, either from common airborne laboratory contaminants (methylene chloride, acetone) or from laboratory water containing VOCs, typically methylene chloride, acetone, and toluene or water disinfection byproducts (chloroform, dichlorobromomethane, chlorodibromomethane, bromoform). Rare, but well documented sources of trip blank and associated field samples contamination are insufficiently clean sample... 

Source National Research Council of the National Academies, Hydrogen chloride Acute exposure guideline levels, Acute Exposure Guideline Levels for Selected Airborne Chemicals, Vol. 4, The National Academies Press, Washington, DC, 2004, 79. 

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