Sea salt particles

Element Windbome Soil Particles Sea Salt Spray Volcanoes Forest Fires Biogenic Sources Total"... 

Air pollutant particles range in size from fly ash particles, which are big enough to see, down to individual molecules, ions, or atoms. Many pollutants are attracted into the water droplets of fog. Solids and liquid droplets suspended in the atmosphere are collectively known as particulates. The solids may be metal oxides, soil particles, sea salt, fly ash from electric generating plants and incinerators, elemental carbon, or even small metal particles. Aerosol particles range upward from a diameter of 1 nanometer (nm) to about 10,000 nm and may contain as many as a trillion atoms, ions, or small molecules. Particles in the 2000-nm range are largely responsible for the deterioration of visibility. 

X10 g year ) as of 1983 among the main natural sources of Hg are wind-borne soil particles, sea salt spray, volcanic activity, forest wildfires, and biogenic emissions (Nriagu 1989). 

Visibility is also affected by alteration of particle size due to hydroscopic particle growth, which is a function of relative humidity. In Los Angeles, California, the air, principally of marine origin, has numerous sea salt particles. Visibility is noticeably reduced when humidity exceeds about 67%. In a study of visibility related to both relative humidity and origin of... 

Although the corrosivity may not be high provided the condensed moisture remains uncontaminated, this rarely happens in practice, and in marine environments sea salts are naturally present not only from direct spray but also as wind-borne particles. Moreover, many marine environments are also contaminated by industrial pollution owing to the proximity of factories, port installations, refineries, power stations and densely populated areas, and in the case of ships or offshore installation superstructures by the discharge from funnels, exhausts or flares. In these circumstances any moisture will also contain S, C and N compounds. In addition, solid pollutants such as soot and dust are likely to be deposited and these can cause increased attack either directly because of their corrosive nature, or by forming a layer on the surface of the metal which can absorb and retain moisture. The hygroscopic nature of the various dissolved salts and solid pollutants can also prolong the time that the surface remains moist. 

Chemical radicals—such as hydroxyl, peroxyhydroxyl, and various alkyl and aryl species—have either been observed in laboratory studies or have been postulated as photochemical reaction intermediates. Atmospheric photochemical reactions also result in the formation of finely divided suspended particles (secondary aerosols), which create atmospheric haze. Their chemical content is enriched with sulfates (from sulfur dioxide), nitrates (from nitrogen dioxide, nitric oxide, and peroxyacylnitrates), ammonium (from ammonia), chloride (from sea salt), water, and oxygenated, sulfiirated, and nitrated organic compounds (from chemical combination of ozone and oxygen with hydrocarbon, sulfur oxide, and nitrogen oxide fragments). ... 

The use of EF values allows us to set limits on possible sources of elements. In Figure 1, EF values for six cities are compared with the ranges for particles from nine coal-fired power plants. For llthophlle elements such as SI, Tl, Th, K, Mg, Fe and many others not shown, E values are close to unity as expected, as these elements have mainly crustal sources, l.e., entrained soil and the aluminosilicate portion of emissions from coal combustion (see Table I). Many other elements are strongly enriched In some or all cities, and, to account for them, we must find sources whose particles have large values for those elements. Some are fairly obvious from the above discussions Pb from motor vehicles, Na from sea salt In coastal cities, and V and, possibly, N1 from oil In cities where residual oil Is used In large amounts (Boston, Portland, Washington). 

In addition, the high concentrations of ions in solutions of high ionic strength such as sea salt particles (especially near their deliquescence point) can alter gas solubility. In this case, the Henry s law constants must be modified using Setchenow coefficients to take this effect into account (e.g., Kolb et al., 1997). 

Figure 5.29 is a schematic diagram of a DRIFTS apparatus that has been applied to studying the reactions of the components of sea salt particles with various oxides of nitrogen. As the reactions occur, nitrate, which absorbs strongly in the infrared, is formed on the salt surface. Since the reactant solids do not absorb in the infrared, the increase in nitrate with time can be readily followed and used to obtain reaction probabilities. 

Alfassi, Z. B S. Padmaja, P. Neta, and R. E. Huie, Rate Constants for Reactions of NO, Radicals with Organic Compounds in Water and Acetonitrile, J. Phys. Chem., 97, 3780-3782 (1993). Allen, H. C., J. M. Laux, R. Vogt, B. J. Finlayson-Pitts, and J. C. Hemminger, Water-Induced Reorganization of Ultrathin Nitrate Films on NaCI—Implications for the Tropospheric Chemistry of Sea Salt Particles, J. Phys. Chem., 100, 6371-6375 (1996). Allen, H. C., D. E. Gragson, and G. L. Richmond, Molecular Structure and Adsorption of Dimethyl Sulfoxide at the Surface of Aqueous Solutions, J. Phys. Chem. B, 103, 660-666 (1999). Anthony, S. E R. T. Tisdale, R. S. Disselkamp, and M. A. Tolbert, FTIR Studies of Low Temperature Sulfuric Acid Aerosols, Geophys. Res. Lett., 22, 1105-1108 (1995). 

De Haan, D. O., T. Brauers, K. Oum, J. Stutz, T. Nordmeyer, and B. J. Finlayson-Pitts, Heterogeneous Chemistry in the Troposphere Experimental Approaches and Applications to the Chemistry of Sea Salt Particles, Int. Rev. Phys. Chem., in press (1999). 

Crutzen and co-workers (Sander and Crutzen, 1996 Vogt et al., 1996) have developed a model for chemistry in the marine boundary layer at midlatitudes, in which autocatalytic cycles involving sea salt particles generate photochemically active gases such as BrCl, Br2, and Cl2. It is likely that such chemistry also occurs in the Arctic as well. In these cycles, reactions (125) and (126) in the condensed phase,... 

However, what remains unknown is the source of the original bromine that initiates the chemistry. There have been a number of hypotheses, including the photolysis of bromoform which is generated by biological processes in the ocean (Barrie et al., 1988) or reactions of sea salt, either suspended in the air or deposited on, or associated with, the snowpack. These include photolysis of BrN02 formed from the reaction of sea salt particles with N2Os (Finlayson-Pitts et al., 1990), the... 

FIGURE 6.38 Schematic diagram of HOBr chemistry with sea salt particles/ice (graciously provided by T. Benter). 

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). 

Mozurkewich, M Mechanisms for the Release of Halogens from Sea-Salt Particles by Free Radical Reactions, J. Geophys. Res., 100, 14199-14207 (1995). 

Airborne sea salt particles are generated by wave action, which produces small droplets of seawater (Blanchard, 1985). As the droplets move inland, water can evaporate from the droplets, leaving a solid suspended particle containing the solids that were originally in the ocean water. 

Hence, other reactions of N02 that could potentially occur in the atmosphere include the reaction with components of sea salt particles such as NaCl and NaBr (e.g., Robbins et al., 1959 Cadle and Robbins, 1960 Schroeder and Urone, 1974 Chung et al., 1978 Sverdrup and Kuhlman, 1980 Finlayson-Pitts, 1983 Zetzsch, 1987 Mamane and Gottlieb, 1990 Winkler et al., 1991 Junkermann and Ibusuki, 1992 Vogt and Finlayson-Pitts, 1994 Karlsson and Ljungstrom, 1995 Vogt et al., 1996 Peters and Ewing, 1996 De Haan et al., 1999) ... 

Figure 7.14 shows the calculated ratio of S(IV) oxidation with the uptake and reaction of N03 to that without the NO, contribution as a function of the chloride concentration in particles (Rudich et al., 1998). For reference, the saturation concentration of Cl- in sea salt particles (i.e., at the deliquescence point) is 6 M at room temperature. Under the assumptions of these particular calculations, the rate of aqueous-phase oxidation of S(IV) is estimated to increase by as much as 25% when N03 chemistry is taken into account. This uptake and reaction of NO, also decrease its gas-phase concentrations. 

FIGURE 7.14 Model-estimated increase in S(IV) oxidation in the aqueous phase of sea salt particles due to the uptake and reactions of NO,. O, taken as 40 ppb, NO, as 0.1 ppb, and H202 as 0.05 ppb. The Y-axis is the calculated ratio of oxidized sulfur, S(VI), formed in droplets when NO, chemistry is included to that when it is not (adapted from Rudich et al., 1998). 

While the hydrolysis of N205 is believed to represent its major loss process, there are other possibilities that have potentially interesting implications under certain conditions. For example, N2Os reacts with the components of sea salt particles such as NaCl, NaBr, and Nal to form nitryl chloride, nitryl bromide, and nitryl iodide, respectively (e.g., Finlayson-Pitts et al., 1989a, 1989b Behnke and Zetzsch, 1990 Zetzsch and Behnke, 1992 Junkermann and Ibusuki, 1992 George et al., 1994 Behnke et al., 1994, 1997 Leu et al., 1995 Fenter et al., 1996 Barnes et al., 1991 Schweitzer et al., 1998) ... 

Finally, in some areas with unique chemical compositions, HN03 may have the opportunity to react with other species as well. For example, it reacts relatively rapidly with NaCl, the major component of sea salt particles ... 

If the relative humidity is above the deliquescence point of NaCl (75% at 25°C), the sea salt particles are... 

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