Deposition of acids

Acid Deposition. Acid deposition, the deposition of acids from the atmosphere to the surface of the earth, can be dry or wet. Dry deposition involves acid gases or their precursors or acid particles coming in contact with the earth s surface and thence being retained. The principal species associated with dry acid deposition are S02(g), acid sulfate particles, ie, H2SO4 and NH HSO, and HN02(g). Measurements of dry deposition are quite sparse, however, and usually only speciated as total and total NO3. In general, dry acid deposition is estimated to be a small fraction of the total... 

In a study of the adsorption of soap and several synthetic surfactants on a variety of textile fibers, it was found that cotton and nylon adsorbed less surfactant than wool under comparable conditions (59). Among the various surfactants, the cationic types were adsorbed to the greatest extent, whereas nonionic types were adsorbed least. The adsorption of nonionic surfactants decreased with increasing length of the polyoxyethylene chain. When soaps were adsorbed, the fatty acid and the aLkaU behaved more or less independently just as they did when adsorbed on carbon. The adsorption of sodium oleate by cotton has been shown independently to result in the deposition of acid soap (a composition intermediate between the free fatty acid and the sodium salt), if no heavy-metal ions are present in the system (60). In hard water, the adsorbate has large proportions of lime soap. 

Solutions of different carboxylic acids (fiimaric acid [FA], maleic acid, acrylic acid, succinic acid, and malonic acid) in ethanol have been effectively used as primers to increase the adhesion of synthetic vulcanized SBRs. The increase in the adhesion properties of SBR treated with carboxylic acid is attributed to the elimination of zinc stearate moieties and the deposition of acid on the rubber which migrates into the solvent-borne polyurethane adhesive layer once the adhesive joint is formed. The nature of the carboxylic acid determines the rate of diffusion into the adhesive and the extent of rubber-adhesive interfacial interaction. 

In a special study, made in charge of the Dutch government a yearly deposition of acids and acidifying compounds was calculated as summarised in table I. 

Table I. Deposition of acid and acidifying compounds 1) in molequiva-lents per ha per year in the Netherlands in the period round 1980.

Although the term acid rain has been used extensively in the popular literature to describe the formation and deposition of acids at the earth s surface, the terminology acid deposition is more commonly encountered in the scientific literature. The reason for this is that deposition of acids can occur either as dry deposition or as wet deposition. The former refers to the direct transport of acidic gases or small particles to the surface, followed by adsorption, without first being dissolved in an aqueous phase such as rain, clouds, or fog. Wet deposition, on the other hand, refers to the transport of acids to, and deposition on, surfaces (including soil, trees, grass, buildings, etc.) after the acids have been dissolved in an aqueous medium. It should be noted that the surface itself can be either wet or dry the terms wet and dry deposition refer to the mechanism of transport to the surface, not to the nature of the surface itself. 

Nguyen, V. D., A. G. A. Merks, and P. Valenta. 1990. Atmospheric deposition of acid, heavy metals and dissolved organic carbon and nutrients in the Dutch delta area in 1980—1986. Science of the Total Environment 99 77—91. 

Sections of eastern North America are being adversely affected by deposition of acidic precipitation and aerosols, generally termed acid rain. Most severely affected are ecosystems which overlie the Canadian Shield, a silicate bedrock with low Mg and Ca... 

Although the mechanism for the production and deposition of acid are not yet fully understood, atmospheric chemists and meteorologists have been studying these problems in depth for the past several years and have made considerable progress. Methods and instruments for reliable measurements of key species in air and clouds have been developed and exploited in field studies. Rates of reactions important in the formation of acids, sulfates, and nitrates have been measured. Huge amounts of reliable field data have been accumulated. Models have been developed and are being tested against bodies of field data. 

Since the mid-1970 s, increasing interest has emerged in the environmental consequences of the large scale deposition of atmospheric contaminants. The deposition of acid-forming constituents, sulfate and nitrate, is of particular concern for potentially adverse ecological effects. These species derive from the oxidation of sulfur dioxide (SO ) and nitrogen oxides (NO and NO ). Over most if... 

Acidification Release of oxides of sulfur and nitrogen (SOx, NOx) Chemical oxidation and deposition of acid compounds Acidic precipitation and lowering of pH in lakes and soils Ecosystem changes and plant/animal death Acidification Potential (AP)... 

They could remove the coat of waxes on the leaf surface, and so then the sea salt could penetrate into the cells and could kill the cells. I just wanted to know if this has been cleared in your country, or is it still in discussion The other point you mentioned quite rightly that NH 4 is no really neutralizing agent. In the soil it will be transformed into NO i, and nitric acid will contribute to acidity. The measurement of total acidity by just titrating the amount of acidity is a questionable thing. You have to determine the species of N0 3 and NH" 4 in the precipitation and add it to the acidity, so you have to do more than titrating... Well, I have a question what happens on the surface of leaves or other material in dry deposition of acids Maybe if you have a coat of SO2 which is then transformed into sulphuric acid, will this sulphuric acid be a permanent coat on the leaves and can nitric acid then be added to this ... 

The mechanism of dry deposition of acid gases on plant surfaces and their results on plants are hard to simulate and are not fully understood. 

A number of observed effects are now with a greater or lesser degree of confidence ascribed to the deposition of acid materials, heavy metals and other species. They include ... 

Numerous experiments have been conducted to understand the chemical linkages between atmospheric deposition of acidic compounds and acidification of soils, lakes, and streams. Experiments have included additions of acid, exclusion of acids, and the application of limestone (CaC03) or other acid neutralizing compounds to add ANC directly to surface water or sods. Many of the studies are discussed in Dise and Wright (1992), Rasmussen et al. (1993), and Jenkins et al. (1995). We highlight a few studies here. 

We conclude tliat enhanced continental weathering occurred at the K/T boundary, and using Sr in forams as a proxy for that weathering, that —1 x 10 equivalents of strong acid were deposited on tlie continents. This, and D Hondt s upper limit to acidification of the oceanic mixed layer, implies preferential deposition of acid to tlie continents, particularly North America... 

Deposition of polyelectrolytes Lajimi et al. [56] explored the surface modification of nanofiltration cellulose acetate (CA) membranes by alternating layer-by-layer deposition of acidic chitosan (CHI) and sodium alginate (AEG) as the cationic and anionic polyelectrolyte, respectively. The supporting CA membranes were obtained by a phase separation process from acetone/formamide. The permeation rate of salted solutions was found to be higher than that of pure water. The rejection of monovalent salt was decreased, while that of divalent salt remained constant so that the retention ratio increased. Increasing the concentration of feed solutions enhanced this selectivity effect. 

Pollutants can enter through direct dumping, piped outflow, and channeled waste streams as localized point sources, or as diffuse nonpoint sources they can enter rivers, lakes, streams, and groundwater through runoff and soil percolation. Nonpoint sources are considered to be major contributors to air, water, and soil pollution which include runoff from paved streets and parking lots, agricultural lots, soil erosion from logging, atmospheric deposition of acidic or toxic air pollutants (Table 1). The source is particularly... 

Acid deposition, the deposition of acidic substances from the atmosphere onto Earth s surface, is another phenomenon associated with atmospheric pollution. Acid rain refers to the low pH of precipitation that has been observed in... 

FIGURE 4-39 The acid deposition process. Acid precursors, notably oxides of nitrogen and sulfur, are emitted to the atmosphere, primarily by fuel-burning equipment. Acid precursors are oxidized in the atmosphere to nitric and sulfuric acids by a variety of homogeneous and heterogeneous reactions. The acids are deposited by precipitation-related processes such as washout and rainout, by sorption of nitric acid vapor, and by dry deposition of acidic particulate material such as ammonium sulfate aerosol. (Stern et ah, 1984.)... 

The dry and wet deposition of acidic sulphur compounds arrives on the soil and on the vegetation. Most rain occurs over land surfaces and washes the pollutants absorbed on vegetation through the soil into freshwater systems. As the rain passes through the soil it is affected by many chemical reactions which can change its composition before it reaches a head-water stream or upland lake. These chemical reactions can be driven by the increased deposition of acidic sulphur compounds and can lead to the acidification of the soils and the freshwaters. Acidified soils are not as productive as weU-buffered soils and have depleted communities of flora and fauna. Acidified freshwaters have depleted fisheries and populations of insects, amphibians, mammals and birds. 

Selecting sensitive receptor sites In the analysis of environmental acidification from sulphur dioxide emissions, an important first step is the selection of possible locations for receptor sites which may be particularly sensitive to the deposition of acidic sulphur species. Table 1 contains the locations of arbitrary receptor sites which have been chosen to reflect the contribution from sulphur deposition to environmental damage caused by the acidification of soils, surface waters and freshwater ecosystems [14]. 

Based on the critical loads maps for the acidification of UK soils and freshwaters by the deposition of acidic sulphur compounds, critical loads of 5 kg S/ha/yr have been adopted to reflect the contribution to environmental damage caused by sulphur deposition in the regions with sensitive geologies selected in Table 1. These estimates are purely illustrative and have been developed to facilitate the analysis. In aU cases it is assumed that both wet and dry sulphur deposition are equally damaging and henceforward the term, total sulphur deposition, refers to their sum. 

In the presence of moisture, it is assumed that the key chemical reactions are initiated by SO2 and perhaps by NOj gases. Other mechanisms, such as dry deposition of acidic aerosol or deposition of HNO to dry surfaces, are not considered. Synergistic effects are similarly disregarded. 

The research being performed to support the National Acid Precipitation Assessment Program (NAPAP) has also led to considerable progress with regard to the other problem areas mentioned above. Damage functions have been developed by analyzing experimental data which delineate the separate effects of dry deposition of SO2 from those of wet deposition of acidity (H ), not only for metals (3 but for paints (O and calcareous stones ( 5). The spatial variability of relative humidity and thus... 

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