Seawater aerosol

Chlorides are often found as the salt aerosols of the atmosphere, and consequently may strongly influence the corrosion performance of structures and plant, particularly in marine or coastal situations. This influence on corrosivity reduces proportionately with distance from the seawater surface, though local environmental factors such as prevailing wind direction, level... 

Eberlein and Kattner [194] described an automated method for the determination of orthophosphate and total dissolved phosphorus in the marine environment. Separate aliquots of filtered seawater samples were used for the determination orthophosphate and total dissolved phosphorus in the concentration range 0.01-5 xg/l phosphorus. The digestion mixture for total dissolved phosphorus consisted of sodium hydroxide (1.5 g), potassium peroxidisulfate (5 g) and boric acid (3 g) dissolved in doubly distilled water (100 ml). Seawater samples (50 ml) were mixed with the digestion reagent, heated under pressure at 115-120 °C for 2 h, cooled, and stored before determination in the autoanalyser system. For total phosphorus, extra ascorbic acid was added to the aerosol water of the autoanalyser manifold before the reagents used for the molybdenum blue reaction were added. For measurement of orthophosphate, a phosphate working reagent composed of sulfuric acid, ammonium molyb-... 

This simple two component model for the Fe isotope composition of seawater does not consider the effects of the Fe isotope composition of dissolved Fe from rivers or from rain. Although the dissolved Fe fluxes are small (Fig. 19) the dissolved fluxes may have an important control on the overall Fe isotope composition of the oceans if they represent an Fe source that is preferentially added to the hydrogenous Fe budget that is ultimately sequestered into Fe-Mn nodules. In particular riverine components may be very important in the Pacific Ocean where a significant amount of Fe to the oceans can be delivered from rivers that drain oceanic islands (Sholkovitz et al. 1999). An additional uncertainty lies in how Fe from particulate matter is utilized in seawater. For example, does the solubilization of Fe from aerosol particles result in a significant Fe isotope fractionation, and does Fe speciation lead to Fe isotope fractionation ... 

Figure 20. Calculated Fe isotope composition of seawater from different ocean basins based on a simple two-component mixing between Fe from aerosol particles and Fe from mid-oceanic-ridge (MOR) hydrothermal solutions. Atmospheric Fe fluxes (Jatm) for different ocean basins from Duce and Tindale (1991) MOR hydrothermal Fe flux ( mor) to different ocean basins were proportioned relative to ridge-axis length. Modified from Beard et al. (2003a).

Zafiriou, O.C. Reaction of methyl halides with seawater and nrarine aerosols, / Mar. Res., 33(1) 75-81, 1975. 

It is likely that there are as yet ill-defined aqueous-phase reactions in the airborne seawater droplets that release photochemically labile chlorine gases. For example, Oum et al. (1998a) have shown that Cl2 is formed when sea salt aerosols above their deliques-... 

Arctic at polar sunrise. The mechanism likely involves regeneration of photochemically active bromine via heterogeneous reactions on aerosol particles, the snow-pack, and/or frozen seawater. The source of the bromine is likely sea salt, but the nature of the reactions initiating this ozone loss remains to be identified. For a review, see the volume edited by Niki and Becker (1993) and an issue of Tellus (Barrie and Platt, 1997). 

The concentration of metals in atmospheric aerosols and rainwater (Table 7.1) is therefore a function of their sources. This includes both the occurrence of the metals in combustion processes and their volatility, as well as their occurrence in crustal dust and seawater. As a result of this, the size distribution of different metals is very different and depends on the balance of these sources. For a particular metal this distinction is similar in most global locations (Table 7.2), although some variability does occur as wind speed and distance from source exert an influence on the particle size distribution spectrum (Slinn, 1983). Once in the atmosphere particles can change size and composition to some extent by condensation of water vapour, by coagulation with other particles, by chemical reaction, or by activation (when supersaturated) to become cloud or fog droplets (Andreae et al., 1986 Arimoto et al., 1997 Seinfeld and Pandis, 1998). 

Figure 7.4 Effect of pH cycling on the dissolution of manganese from crustal aerosols under conditions likely both in the atmosphere and on mixing into seawater (Spokes and Jickells, 1996). Manganese shows high solubility at a typical cloud water pH of 2. Solubility decreases slightly at rainwater pH of 5.5 and rapidly at pH 8. Extensive solution phase removal is not seen at pH 8 under conditions designed to mimic seawater, perhaps due to the formation of soluble MnCI+ and MnSOl-. Low pH cycling and inorganic complexation under seawater conditions increase manganese solubility six times over that seen at pH 8 alone.

So what is the fate of this dissolved iron in rainwater and the labile iron on aerosol surfaces upon deposition to seawater Based on the results of acid cycling... 

Maring, H.B. and Duce, R.A. (1987) The impact of atmospheric aerosols on trace metal chemistry in open ocean surface seawater. 1. Aluminium. Earth Planet. Sci. Letts, 84, 281-392. 

Spokes, L.J. and Jickells, T.D. (1996) Factors controlling the solubility of aerosol trace metals in the atmosphere and on mixing into seawater. Aquat. Geochem., 1, 355-374. 

In this chapter, we examine biogeochemical applications of the FREZCHEM model to Earth, Mars, and Europa, where cold aqueous environments played and continue to play a critical role in defining surficial geochemistry. Interpretations include the potential for life in these environments. These simulations cover applications to seawaters, saline lakes, regoliths, aerosols, and ice cores and covers. These examples are the proverbial tip of the iceberg in terms of the potential of this model to describe cold aqueous geochemical processes. At the end of the chapter, we discuss application limitations, cases where the underlying thermodynamic assumptions are at variance with real-world situations. 

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