Sea salt concentrations

Sea Salts - Most of the Na and Cl in both Greenland and Antarctica is of marine origin [1,13,21]. Near the ocean, sea salts may also account for most of the Mg, K, Ca, and S042-. Concentrations of Na and Cl display a maximum in winter Greenland precipitation which is coincident with the minimum oxygen isotope delta values [1,13,18]. The seasonal maximum in sea salt concentrations may be due to increased storminess, over the ocean in winter or to an increased poleward latent heat flux during the polar night [13]. 

The loss of resolution of seasonal variations in sea salt concentrations near the ocean may be interpreted to reflect the presence of two marine sources with different seasonal maxima. A distant source with a winter maximum, as in the case in Greenland, dominates for more inland stations like J-9. Nearer the ice front, the local Ross Sea contribution is greatest in the summer when the sea ice cover is at a minimum. The contribution from the... 

Manders AMM, Schaap M, Querol X et al (2010) Sea salt concentrations across the European continent. Atmos Environ 44 2434—2442... 

At a sea salt concentration totaling 3.5 wt%, using the thermodynamic data of Dholabhai et al. (1991) in Chapter 6, a pressure of 4.364 MPa (a minimum seawater depth of 436 m—about 55 m deeper than in pure water) is required to stabilize hydrates at 277 K. Further corrections to the phase boundary are required considering effects of (1) hydrocarbons other than methane, (2) salt concentrations other than 3.5 wt%, and (3) sediment pores or capillary pressure, as indicated in Chapter 5. 

Figure 3 shows that a usable, though nonlinear, calibration may be obtained down to 1 x 10 M chloride. Table II shows sampling requirements calculated on the basis of reasonable estimates of pumping speed and aerosol concentration. These requirements assume a 10-mL sample size. Useful sea-salt concentration data with 8-min sampling periods can be obtained even at wind speeds well below I m/s. Apparently, then, the requirement for collecting data at a rate sufficient for investigation of shortterm variations can be met. 

Residence Time. If the salt peak on Julian Day 45 at 0900 is due to continually sampling the same air mass, the residence time is 19 h. [Residence time is defined as the time for the salt concentration to drop to low values following a wind speed drop (5).] Lovett s (5) observations of the time variation of sea-salt concentration and wind speed indicated residence... 

The data and arguments presented indicate that the presence of sea salts alters the atomic absorption signal of these four elements from their response in de-ionized water-acid standards in a consistent manner for each particular element and sea salt concentration. This observation can be used to develop a modified standard addition technique. If a series of curves can be prepared that contain the range of metal and sea salt concentration expected in the samples, correction factors between actual and observed concentrations based on pure water-acid standards can be determined. This modified standard addition technique is illustrated for two of the elements discussed previously. For lead the actual concentration is plotted vs. the calculated concentration for a sea salt range of 1.0-5.0 parts per thousand sodium in Figure 4. This plot was prepared from solutions of known concentrations in a sea water medium. For a sample of unknown lead concentration, within the specified range. 

The quantity of sea salt particles, identified as NaCl, was found to be particularly important over the Indian Ocean. This is explained by stormy weather conditions during the sampling period. Curve 1 in Fig. 35 gives the size distribution of sea salt particles measured over the Indian Ocean (the total number concentration, N, is also plotted). T o represent the ad vection of sea salt particles over the continents, two other spectra are also shown. Curve 2 was measured by Metnieks (1958) in Ireland while distribution 3 was observed in the surface air in Hungary (E. Meszaros, 1964). These latter investigators used gelatin layers sensitized with silver nitrate to identify chloride particles. Figure 35 makes clear that the sea salt concentration is very small... 

The estimate for sea salt goes back to a detailed study of Eriksson (1959) of the geochemical cycles of chloride and sulfur. He calculated the rate of dry fallout of sea-salt particles from a vertical eddy diffusion model and then existing measurements of sea-salt concentrations over the ocean. This led to a global rate for dry deposition of 540 Tg/yr. Eriksson then argued that wet precipitation would remove a similar amount annually. It is now known, however, that wet precipitation is more effective than dry deposition in removing aerosol particles from the atmosphere, so that Eriksson s value must be an underestimate. The discussion in Section 10.3.5 suggests a flux rate for sea salt of about 5,000 Tg/yr. 

The low amount of liquid water associated with particles (volume fraction 10 compared to clouds, for which the volume fraction is on the order of 10 ) precludes significant aqueous-phase conversion of SO2 in such droplets. These particles can contribute to sulfate formation only for very high relative humidities (90% or higher) and in areas close to emissions of NH3 or alkaline dust. Sea-salt particles can also serve as the sites of limited sulfate production (Sievering et al., 1992), as they are buffered by the alkalinity of seawater. The rate of such a reaction as a result of the high pH of fresh sea-salt particles is quite rapid, 60/xMmin corresponding to 8% h for the remote oceans (SO2 = 0.05 ppb). Despite this initial high rate of the reaction, the extent of such production may be quite limited. For a sea-salt concentration of 100 nmol m the alkalinity of sea-salt is around 0.5 nmol m . Consequently, after 0.25 nmol m of SO2 is taken up in solution and oxidized, the initial alkalinity would be exhausted and the reaction rapidly quenched as the pH would immediately decrease. 

Most particles larger than 600 nm are essentially sea salt. However, sea salt is found primarily in the coarse mode, except during episodes of continental dust transport. Sea salt concentrations are about 1-20 jxg m at surface level (40). 

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