Salt, chemical composition marine aerosol

Relative Chemical Composition of Marine Aerosol Salt... 

In many instances the chemical composition of oceanic rain has been used to draw conclusions concerning the chemical composition of marine aerosols (3, 52, S3, 54). The first two entries in Table V emphasize the trends with respect to altitude for our data on rain samples collected in Hawaii. The 100-meter sample was collected near the coast, and the 1000-meter sample was obtained several miles inland in the Hawaiian mountains. The results for F/Cl, Cl/Na, and Na/F in the 100-meter sample agree with the results found for marine aerosol salt fractions given in Table II, and differ only slightly from those of sea water. 

Several workers (39, 49, 50) have shown that the atmospheric concentration of salt derived from the ocean surface decreases rapidly to small values at an altitude of about 2 km. Are there also changes in chemical composition in the salt fraction of the marine aerosol with... 

Study (4, 52). The aerosol salt composition may be further modified when the droplets are carried to higher altitudes where they lose water by evaporation, crystallize, and then lose other constituents such as chlorine gas (12, 26,64). Another possibility of change in the chemical composition is the reaction of the aerosol salt with atmospheric gases such as elemental iodine, which originates at the ocean surface (65). In addition, soluble particles are produced from gaseous compounds in the marine atmosphere, such as the production of (NH4)oS04 via the atmospheric oxidation of SO-j (9). 

Because a great variety of sources contribute materials to the tropospheric aerosol, it represents a complex mixture of marry substances that additionally depends on the size of the particles. Source characteristics are preserved only in the vicinity of somces. The mixtirre may be divided into three fractiorts water-solirble inorganic salts (electrolytes), water-irrsoluble minerals, and organic compoimds, both soluble in water and insoluble. Table II shows the chemical composition of two boimdary layer aerosols that are typical of marine and of rural continental air. 

In connection with the determination of transboundary fluxes and deposition of air pollutants, the concentrations of sulfate, ammonium, and nitrate in precipitation are particularly important. However, determination of one or more sea-salt constituents (Na, Cl, and Mg) is also necessary in order to determine the fraction of the sulfate concentration due to marine sea-spray aerosols. Moreover, determination of the base cations Ca, K, and Mg is desirable in order to obtain an indication of the large-scale deposition of bases this is needed in connection with the determination of critical loads. Finally, pH and conductivity should be determined in order to obtain some idea of the overall composition of the samples, and to check the consistency of the chemical analyses. 

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