Sea-salt sulphate

O Dowd, C. D., J. A. Lowe, and M. H. Smith, Biogenic Sulphur Emissions and Inferred Non-Sea-Salt-Sulphate Cloud Condensation Nuclei in and around Antarctica, J. Geophys. Res., 102, 12839-12854 (1997a). 

In the atmosphere DMS is oxidised mainly in the gas phase. Oxidation in cloud-water droplets is insignificant as the low solubility of DMS mitigates the effects of its rapid aqueous oxidation by ozone ( , McElroy, W.J., Central Electricity Research Laboratories, personal communication). Gas-phase oxidation is initiated principally by reaction with OH radicals ( ) and methanesulphonic acid (MSA) is one of the products (2). MSA has a very low vapour pressure and will be rapidly scavenged by aqueous aerosols and cloud droplets wherein further oxidation to sulphate by OH may occur. Although the kinetics and mechanism of this process have yet to be unambiguously determined, it is possible that emissions of DMS could be both a significant source of "background" sulphur and, upon oxidation, of non sea-salt sulphate. 

The current version of GEM-AQ has five size-resolved aerosols types, viz. sea salt, sulphate, black carbon, organic carbon, and dust. The microphysical processes which describe formation and transformation of aerosols are calculated by a sectional aerosol module (Gong et al. 2003). The particle mass is distributed into 12 logarithmically spaced bins from 0.005 to 10.24 pm radius. This size distribution leads to an additional 60 advected tracers. The following aerosol processes are accounted for in the aerosol module nucleation, condensation, coagulation, sedimentation and dry deposition, in-cloud oxidation of SO2, in-cloud scavenging, and below-cloud scavenging by rain and snow. 

Fig. 7.19 Time series (1987-1991) of weekly average concentrations of methane sulphonic acid (MSA), non-sea-salt-sulphate (nss-SCT) and ammonium (NHJ) measured at Mawson, Antartica. After Savoie et al. (1993), with kind permission of Kluwer Academic Publishers.

In Fig. 7.19 atmospheric measurements of particulate MSA, SO4" (after subtraction of the component coming from sea salt, the so-called non-sea-salt-sulphate (nss-SO )) and NHJ made in air at Mawson in Antarctica are shown. This site is very remote from human activities and typically receives air which has blown over thousands of kilometres of the Southern Ocean before being... 

Fig. 7.24 150000-year record of methane sulphonic acid (MSA) concentration, non-sea-salt-sulphate (nss-SOj-) aerosol concentration and temperature reconstruction (from oxygen isotope data) from an Antarctic ice core. MSA and nss-SOj" aerosol concentrations are both high during very cold conditions, e.g. the last glacial period between 18 and 30 thousand years ago (see text for discussion). After Legrand et id. (1991). 

Recently, several articles have appeared on the combined use of different other microanalysis techniques for atmospheric aerosols. Let us mention one. Hopkins et al. successfully used CC SEM/EDX, time-of-flight secondary ion mass spectrometry (TOF-SIMS) and scanning transmission X-ray microscopy/near-edge X-ray absorption fine structure analysis (STXM/NEXAFS) to study quantitatively methanesulphonate (CHsSOs") and non-sea salt sulphate in individual marine aerosol particles. This indicated e.g. that CHsSOs" salts were the dominant source of non-seasalt sulphur in large particles, while sulphate was more common in smaller particles. Quantitative assessment of these two forms is important for kinetic modelling concerning the pathways of natural dimethylsulphide oxidation and the impact on the number and size of cloud condensation nuclei in the marine environment. 

Recent measurements of total sulphide in sea water show concentrations of about InM (Cutter and Krahforst, 1988) but how much of this is as free sulphide and hence available for exchange into the atmosphere is not clear. Using simultaneous DMS and H2S measurements Saltzman and Cooper (1988, 1989) suggest that H2S emissions may contribute about 10% of the non-sea salt sulphate in marine air but caution against the extrapolation of these data to the world ocean. Unfortunately there are too few data available at the present time to give a representative picture of temporal and spatial variations in H2S concentrations and emission rates. 

Saltzman ES, Savoie DL, Prospero JM and Zika RG, 1986, Non-sea salt sulphate in Pacific air Regional and seasonal variations. J.Atmos. Chem., 4, 227-240. 

The emission of sea salt is mainly dependent on wind speed. It is considered the second largest contributor in the global aerosol budget, as a vast area of the earth consists of sea. The aerosols consist mainly of sodium chloride. Other constituents of atmospheric sea salt reflect the composition of sea water (magnesium, sulphate, calcium and potassium). Sea salt is the only pure natural aerosol component. 

The reason why SIA is higher in urban areas is less obvious as these are secondary aerosols. The observed increment is predominantly caused by more nitrate and sulphate. The reaction of nitric acid and sulphuric acid with the sea-salt aerosol in a marine urbanised environment follows an irreversible reaction scheme. In essence, the chloride depletion stabilises part of the nitrate and sulphate in the coarse mode and may partly explain part of the observed increment. However, it also raises the question how to assign the coarse mode nitrate in the mass closure. The sea salt and nitrate contributions cannot simply be added any more as nitrate replaces chloride. Reduction of NOx emissions may cause a reduction of coarse mode nitrate, which is partly compensated by the fact that chloride is not lost anymore. A reduction would yield a net result of ((N03-C1)/N03 = (62-35)/62=) 27/62 times the nitrate reduction (where the numbers are molar weights of the respective components), and this factor could be used to scale back the coarse nitrate fraction in the chemical mass balance. A similar reasoning may be valid for the anthropogenic sulphate in the coarse fraction. Corrections like these are uncommon in current mass closure studies, and consequences will have to be explored in more detail. 

First, the SILAM model (Sofiev et al. 2006) was applied in adjoint mode to identify the potential sources of pollution. It was found that the aerosol peak of May 2-3 most probably originated from the Nikel metallurgy factory (Kola Peninsula, Russia) located about 200 km north from Varrio (Kaasik et al. 2007). Then the SILAM model was applied in a forward mode comparatively with the ECMWF and HIRLAM (FMI) meteorological datasets EMEP emission data on sulphate and PM, sea salt emissions calculated by SILAM, emission model based on... 

Smaller acidic sulphate particles may lose chloride and nitrate ions in the form of gaseous hydrochloric and nitric acid. Thus, the chloride in airborne sea salt may be driven off as hydrochloric acid, which may be subsequently absorbed by larger, less acidic particles. Similar chemical reactions can also take place in samples of particles collected on filters, particularly if the coarse and fine particles are not separated. The pressure drop across the filter may also cause evaporation of the more volatile components. The chemical analysis of the collected particles may then give a distorted picture of the true airborne composition of the aerosol. 

Ammonlacal secret salt of giaubar Sea ammonium sulphate. 

But the admirable researches of Gay-Lussac and of Mitscherlich have established the fact, that in many instances, different compounds assume the same form. Thus, the following substances, and many others, take the form of the cube, tetrahedron, or regular octohedron, which are geometrically connected. Chloride of sodium (sea-salt), chloride of potassium, sal ammoniac bromide of potassium iodide of potassium sulphuret of lead fluoride of calcium bisnlphuret of iron arseniuret of cobalt sulphate of alumina and potash (alum) ammonia alum chrome alum, iron alum sesqnioxide of iron, sesquioxide of aluminum, sesquioxide of chromium. In like manner, other crystalline forms are found to be common to many different compounds, although none occurs so frequently as the cube and its congeners. 

When water becomes so highly charged with foreign matters as to have an unpleasant taste, or to acquire medicinal virtues, it is called mineral water. Of mineral waters there are several kinds those in which iron predominates are called chalybeate waters where sulphur prevails, they are called sulphureous waters acidulous waters are those which contain much free carbonic acid and saline wafers are such as contain neutral salts, generally sea salt, and sulphate of magnesia, or Epsom salt. 

When the term salt was first extended beyond sea-salt, the original t rpe, it was applied to substances having similar properties, such as solubility, neutralily, and saline taste, with the property of crystallising. It was found, after a time, that salts were produced by the combination of acids with alkalies, or at least by bringing them together, and as sea-salt was obtained when soda and muriatic acid were mixed, it was supposed to be formed of these constituents, just as sulphate of soda was supposed to consist of sulphuric acid and soda. 

But when, in process of time, it came to be known that sea-salt contained neither muriatic acid nor soda, it was found necessary, since it was impossible to deny the claim of sea-salt to rank as a salt, to admit two kinds or classes of neutral salts, one formed of an oxygen acid and an oxygen base the other, of a salt-radical and a metal. Thus, while sulphate of soda was NaO, SOj sea-salt was Na Cl the former corresponding to the hydrated acid, HO, SO3 the latter to the hydrogen acid, HCl. This, indeed, is the view which has for many years prevailed. 

Sulphate of soda, or Glauber s salt, forms large prisms, the formula of which is Na O, SO3-I-IO aq. or Na, SO,+10 aq. It is used as a laxative and from this salt in its anhydrous state (prepared from sea-salt by the action of oil of vitriol), carbonate of soda is manufactured by heating it with charcoM in a reverberatory furnace. 

Carbonate of soda, Na O, G O, - - 10 aq., forms very large rhomboidal crystals, which effloresce in the air. It was formerly extracted from kelp, or barilla, which is the ashes of marine plants but is now made from sea-salt, far more cheaply, and in a state of perfect purity. The salt, Na Cl, is first converted into sulphate of s(da, Na O, SO, by being heated with oil of vitriol. The sulphate of soda is now mixed with sawdust and lime, and heated in a reverberatory furnace. By this means the sulphuric acid is decomposed, its sulphur partly uniting with c cinm, and partly esc ing as sulphurous acid, while the carbonic acid which is formed unites with soda. The carbonate is purified by crystallisation, but generally retains a trace of sulphuric acid. 

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