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Environmental Pollution

Volume 110, Issue 1, October 2000, Pages 89-102

Acid rain and acidification in China: the importance of base cation deposition

Author links open overlay panelT.LarssenaG.R.Carmichaelb

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Acid deposition has been recognized as a serious environmental problem in China. Most acid deposition studies have focused on sulfur deposition and the pH of precipitation. However, as high concentration of alkaline dust is an important feature of the atmosphere in large parts of China, base cation deposition must be taken into account when discussing possible effects on soils and vegetation from acid deposition. We estimate the deposition of sulfur as well as calcium, i.e. the dominating anion and cation, on a regional scale in China using data both from measurements and modeling. The ratio of sulfur/calcium in deposition is then used as an indicator for identifying areas where deposition acidity exceeds alkalinity, and where soils may be at risk to acidification. The dynamic soil acidification model MAGIC is applied with data from two sites receiving high deposition loads in southwest China. The model predictions indicate that considerable soil acidification has been going on for the last decades due to acid deposition inputs. Effects on the spatial distribution of acidic deposition in China, using different future deposition scenarios, are illustrated. As the size of the anthropogenic fraction of the base cation deposition is unknown, different possible future trends in calcium deposition were used. Soil response, according to the model, using different combinations of sulfur and calcium deposition scenarios is shown. Applying the most strict measures to reduce sulfur emission will almost eliminate the acid deposition problem; however, such a scenario is not economically feasible in the short term. A strict, but possibly realistic, future scenario for sulfur may be enough to keep the situation at the present level, assuming only moderate reductions in calcium deposition. With large decreases in base cation deposition, increased soil acidification can be expected even with considerable sulfur emission reductions.

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Wear

Volumes 233–235, December 1999, Pages 25-38

Rain impact retrospective and vision for the future

Author links open overlay panelWilliam FAdler

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https://doi.org/10.1016/S0043-1648(99)00191-XGet rights and content

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Rain impact effects on aerospace vehicle components have presented challenging problems for investigation in experimental physics, analytical and computational mechanics, fracture mechanics, and systems analysis. The term "rain impact" is used in preference to the more common term "rain erosion", since the resulting damage is not always an erosion process. The significant advances made by the author over the past 25 years in understanding the damaging aspects of liquid drop impingement are described. The perspective is subjective based on the author's view of what was required and what was done to satisfy the need. This background is used to introduce the work that still needs to be done, in the author's view, to provide meaningful estimates of the response of materials during flights through hydrometeor environments. The purpose of this discourse is to appreciate the lessons learned and to stimulate interest in making further progress in a fascinating area of research. How realistic is our understanding of the sequence of events that takes place in the flight environment? How well can the physical concepts of raindrop impacts be represented in a computational form for predicting rain impact damage? What experimentation (simulation or material property evaluation) is required to establish a component's rain impact damage response? Do the existing testing capabilities provide data that is relevant to the flight environment? These are the issues considered based on the author's past experience.

This review describes the more important features of the emission, chemistry, transport and deposition of pollutants involved in acid deposition. Global emissions, both natural and man-made, of sulphur and nitrogen oxides are discussed and examples of spatial distributions and trends over the last century presented. The more significant chemical and physical processes involved in the transformation of the primary emissions into their acidic end products are described, including a summary of the approximate timescales of the processes involved. Measurements and modelled calculations of spatial and temporal patterns in the deposition of acidic pollutants by both wet and dry pathways are presented

6.3.2 Surface-water quality parameters

Surface water comprises rainfall, runoff, base flow, and so on. Each of these inputs to the surface-water system can contribute natural compounds of relevance to water quality. For example, rainfall in highly industrialized regions may consist of acidic precipitation that is introduced to the surface water; runoff may bring with it natural organics, sediments, and so on; and base flow may have elevated levels of hardness from the flow of the water through the subsurface. Human activities may increase the concentration of existing compounds in a surface water or may cause additional compounds to enter the surface water. For example, discharge of wastewater (treated or otherwise) greatly adds to the organic loading of the surface water and clearing of land (for construction, farming, etc.) that can result in increased erosion and sediment load in the surface water. Thus, it is important to recognize the natural (background) quality of surface waters and the existing impacts of human activities on this water quality.

"Surface-water pollution" can be defined in a number of ways. However, most definitions address excessive concentrations of particular substances for sufficient periods of time to cause identifiable effects. "Water quality" can be defined in terms of the physical, chemical, and biological characterization of the water. Physical parameters include color, odor, temperature, solids (residues), turbidity, oil content, and grease content. Each physical parameter can be broken down into subcategories. For example, the characterization of solids can be further subdivided into suspended and dissolved solids (size and settleability) and organic (volatile) and inorganic (fixed) fractions. Fig. 6.2 depicts a hierarchy of different solid tests. Chemical parameters associated with the organic content of water include biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), and total oxygen demand (TOD). It should be noted that BOD is a measure of the organics present in the water; it is determined by measuring the oxygen necessary to biostabilize the organics (oxygen equivalent of the biodegradable organics present). A BOD response curve is shown in Fig. 6.3. Inorganic chemical parameters include salinity, hardness, pH, acidity, alkalinity, and the presence of substances including iron, manganese, chlorides, sulfates, sulfides, heavy metals (mercury, lead, chromium, copper, and zinc), nitrogen (organic, ammonia, nitrite, and nitrate), and phosphorus. Biological properties include bacteriologic parameters such as coliforms, fecal coliforms, specific pathogens, and viruses. Table 6.6 provides an overview of various types and sources of water quality characteristics.

Fig. 6.2. Relationships of various solid tests used for water quality characterization.

Fig. 6.3. BOD response curve.

Table 6.6. Physical, chemical, and biological water quality characteristics and their sources

CharacteristicsSourcesPhysical propertiesColorDomestic and industrial wastes, natural decay of organic materialsOdorDecomposing wastewater, industrial wastesSolidsDomestic water supply, domestic and industrial wastes, soil erosion, inflow/infiltrationTemperatureDomestic and industrial wastesChemical constituentsOrganicCarbohydratesDomestic, commercial, and industrial wastesFats, oils, and greaseDomestic, commercial, and industrial wastesPesticidesAgricultural wastesPhenolsIndustrial wastesProteinsDomestic, commercial, and industrial wastesPriority pollutantsDomestic, commercial, and industrial wastesSurfactantsDomestic, commercial, and industrial wastesVolatile organic compoundsDomestic, commercial, and industrial wastesOthersNatural decay of organic materialsInorganicAlkalinityDomestic wastes, domestic water supply, groundwater infiltrationChloridesDomestic wastes, domestic water supply, groundwater infiltrationHeavy metalsIndustrial wastesNitrogenDomestic, commercial, and industrial wastespHDomestic, commercial, and industrial wastesPhosphorusDomestic, commercial, and industrial wastes; natural runoffPriority pollutantsDomestic, commercial, and industrial wastesSulfurDomestic water supply, domestic, commercial, and industrial wastesGasesHydrogen sulfideDecomposition of domestic wastesMethaneDecomposition of domestic wastesOxygenDomestic water supply, surface-water infiltrationBiological constituentsAnimalsDecomposition of domestic wastesPlantsDecomposition of domestic wastesProtistsEubacteriaDomestic wastes, surface-water infiltration, treatment plantsArchaebacteriaDomestic wastes, surface-water infiltration, treatment plantsVirusesDomestic wastes

Source: Metcalf and Eddy, 1991. Wastewater Engineering-Treatment, Disposal and Reuse, third ed. McGraw-Hill Book Company, New York.

In evaluating surface-water pollution impacts associated with the construction and operation of a potential project, two main sources of water pollutants should be considered: nonpoint and point. Nonpoint sources are also referred to as "area" or "diffuse" sources. "Nonpoint pollutants" refer to those substances that can be introduced into receiving waters as a result of urban area, industrial area, or rural runoff, for example, sediment, pesticides, or nitrates entering a surface water because of runoff from agricultural farms. Point sources are related to specific discharges from municipalities or industrial complexes, for example, organics or metals entering a surface water as a result of wastewater discharge from a manufacturing plant. In a given body of surface water, nonpoint source pollution can be a significant contributor to the total pollutant loading, particularly with regard to nutrients and pesticides. Fig. 6.4 illustrates the relationship between land usage and these pollution sources relative to the resulting quality of receiving waters.

Fig. 6.4. Schematic diagram of the land use/water quality relationship (Shubinski and Tierney, 1973).

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Air Pollution

King EdwardII, in Environmental Pollution and Control (Fourth Edition), 1998

EFFECTS ON MATERIALS

Perhaps the most familiar effect of air pollution on materials is the soiling of building surfaces, clothing, and other articles. Soiling results from the deposition of smoke on surfaces over time as surfaces become discolored or darkened. Cleaning of exterior building materials requires sandblasting that can damage or remove part of the building surface.

Acidic precipitation and pollutants like sulfur dioxide can accelerate the corrosion of metals. Ozone and PAN have resulted in rubber cracking, which can be used to measure ozone concentration (Chapter 20).

Fabrics are also affected by air pollutants. Cities like New York that exhibited high airborne SO2 concentrations because high sulfur content oil was burned for power generation had air sufficiently acidic to cause nylon stockings to run. Fabrics and dyes also bleach and discolor under the influence of various pollutants.

Hydrogen sulfide, in the presence of moisture, reacts with lead dioxide in paint to form lead sulfide, producing a familiar brown to black discoloration.

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NEW DEVELOPMENTS IN ACID PRECIPITATION RESEARCH

J. HARTE, in Energy, Resources and Environment, 1982

ECOLOGICAL AND HUMAN CONSEQUENCES

To predict ecological effects of toxic substances, ecotoxicologists have relied traditionally upon a combination of field studies and laboratory single-species bioassays (15). In recent years the use of ecosystem microcosms has been proposed to augment the traditional tools (16). Microcosms are segments of natural ecosystems of a size convenient for laboratory study. The advantage of toxicology studies in microcosms over laboratory single-species bioassays is that microcosms possess many of the complex features of natural systems that cannot be investigated by studying a single organism in a contrived environment. Among these complex features, the microbe-detritus-nutrient interactions are particularly suited to microcosm investigation and are both critical to ecosystem function and sensitive to a number of toxic substances. The advantage of microcosm investigations over field investigations is that the former are generally easier and less expensive to carry out; moreover microcosms allow replicability and control of experimental conditions.

Although the use of microcosms for study of toxicological effects is in its infancy, several completed studies have provided new and predictive information about chemical and biotic changes in aquatic ecosystems (17,18). In an investigation by K. Tonnessen, a graduate student in the Energy and Resources Program at U.C. Berkeley, effects of acidification on lakes of the California Sierra Nevada were studied. Impacts of a pH reduction on phytoplankton and zooplankton populations, and on alkalinity and trace metal concentrations were quantified. In addition, she has demonstrated how microcosms can be used to obtain useful information about the time frame over which real lakes will lose their buffering capacity and acidify. We expect the microcosm approach to be used increasingly in the future to obtain quantitative and predictive information about ecological impacts of a wide variety of toxic substances.

The human consequences of acid precipitation can be divided conveniently into five categories, ordered here by decreasing ease of assigning monetary cost but not necessarily by decreasing magnitude of impact.

(1)

Direct damage to materials. Acid precipitation can erode buildings and statuary, damage painted surfaces, and corrode synthetic products.

(2)

Damage to natural resources of direct commercial or recreational value. Fish populations have been reduced severely in lakes of southern Scandinavia and the Adirondack Mountains of New York State, USA (8). Commercial and recreational losses result. Clear and irrefutable evidence for damage to forest and agricultural crop productivity from acid precipitation is lacking, but studies suggest the likelihood that continuing acidic precipitation may cause short-term enhanced growth (under certain nutrient-limited circumstances)and long-term decline in productivity. More research is needed to resolve the large uncertainties in this area.

(3)

Effects on human health. The concentration of certain hazardous trace metals is increased in acidified waters by a process of accelerated mobilization of these metals from soils and lake and river sediments. The effect is exacerbated when acidified water flows through metal water pipes carrying drinking supplies. While the phenomenon of metal mobilization by acidified surface waters has been amply documented (8,19), further research is needed to identify the circumstances under which human impacts would be likely to occur. Other direct effects of acid precipitation on human health, particularly on respiratory function, are most likely to arise in urban areas where acid rain, mists, and fogs occur with pH ≤ 3 on occasion (6,20).

(4)

Damage to human services derived from healthy ecosystems. These are the most difficult to investigate and quantify, but their impact could also be the most profound. Healthy ecosystems sustain a number of life-supporting processes vital to human well-being. These include the cycling of nutrients, the purification of air and water by natural biological processes, the modulation of local weather and global climate, the maintenance of a genetic "library," the maintenance of a protective ozone layer in the stratosphere (by the denitrification process), and many others (21,22). An example that is particularly pertinent to the acid precipitation problem is the role of nitrogen-fixing organisms in supplying nitrogen in useful form to certain ecosystems and agricultural crops. In alpine ecosystems and in the tundra, nitrogen fixing lichens are so vital to the functioning of the plant and animal communities that they are called "keystone" species – if they are damaged the entire ecological edifice can tumble. In the Alaskan tundra, for example, the nitrogen supply to off-shore fisheries is supplied largely from terrestrial nitrogen-fixing lichen populations. Because the rate of nitrogen fixation slows under acidic conditions (23), acidic precipitation in the tundra could exert a profound effect on offshore fishing. Thus, there is an indirect ecological link between the lichen and an important commercial activity; study of direct effects of acids on the fish and shellfish would not have revealed this threat. A similarly profound effect could occur in high-mountain ecosystems, such as watersheds in the high Colorado Rockies, where lichens probably are a keystone species and acid precipitation is presently falling (2,7).

The search for keystone species that are sensitive to acid precipitation or other anthropogenic toxicants has just begun. Considerable research is needed to discover linkages such as the one just described. A combination of field research and laboratory studies with microcosms will be needed to do justice to the complexity of the problem. Because of the strong linkages between ecosystem services and human well-being, it is most critical that this subject be further investigated.

(5)

Effects on International Relations. Because of its unique character, this topic is taken up in the follow section.

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Models for the assessment of biofilm and encrustation formation on urological materials

B.F. GILMORE, ... H. CERI, in Biomaterials and Tissue Engineering in Urology, 2009

3.5 Batch flow or 'static' models

The models described below are referred to in the literature as 'static' models. However, these models employ a batch culture, where turnover of fluid is not constant; shear force is created in these models to emulate the flow of urine as would be seen in a catheter system, hence these are not truly static models. Tunney et al.50 described a batch artificial urine model for the study of urinary encrustation in the upper urinary tract. The reaction vessel, as shown in Fig. 3.4, consists of a Perspex tank, with a loose-fitting lid. The artificial urine employed in this model is based on that described by Cox et al.46 but with substantially reduced albumin content. Solutions are added separately to the reaction vessel to prevent acidic precipitation of brushite. The artificial urine (5.16 1) is stirred by means of Teflon-coated metal stirring bars to induce shear force on the catheters, as would be seen in a flow system. A plastic grid is positioned 80 mm above the tank floor from which biomaterial sections (length, 50 mm) are suspended in the artificial urine by means of colour-coded, plastic-coated paper clips. This allows several biomaterials to be evaluated concurrently. An aperture in the plastic grid permits daily solution exchange – 11 is removed daily using a siphon pump and replaced with an equivalent volume of pre-heated (37 °C) artificial urine. Twice weekly, 160 ml is removed and replaced with an identical volume of a third solution containing urease. Sections are removed at defined test periods (i.e. 2, 6 and 14 weeks), rinsed with deionized water, and the type and quantity of encrustation determined by infrared spectroscopy, X-ray diffraction spectroscopy, energy dispersive X-ray analysis and atomic absorption spectroscopy. This model permits large numbers of biomaterials to be evaluated simultaneously and over extended time periods.50 Results from this study indicated that the type of encrustation produced on polyurethane stents in vitro was composed primarily of struvite and hydroxyapatite, and was similar to that produced on stents in vivo.10

3.4. The static artificial urine model for assessment of biomaterial encrustation.

Adapted from Tunney et al.50

In a similar model Jones et al.60 describe a batch, artificial urine bladder encrustation model to study the effects of the components of artificial urine and urease inhibitors on encrustation produced on commercially available stent materials. In essence, the model consisted of a 700 ml-capacity plastic reaction vessel with a firmly attached lid. A schematic diagram of the bladder encrustation model is shown in Fig. 3.5. Sections (2.5 cm) of the ureteral stents were dissected, heat-sealed at both ends and suspended into the artificial urine using Microlance 3 needles (60 mm length) which were firmly attached within the vessel. An aperture on the reaction vessel lid permitted daily replacement of (120 ml) artificial urine. The vessel(s) were placed in an orbital shaker and their contents were exposed to a physiological temperature of 37.0 ± 0.1 °C and a rotation speed of 100 rotations/min. The composition of the artificial urine used in this study was adapted from Tunney et al.50 After 7 days, the masses of calcium and magnesium encrustation on the surface of the stents were quantified by atomic absorption spectroscopy. The model was used to examine the effects of individually altering the concentrations of calcium chloride hexahydrate (0–0.53% w/v) and chicken ovalbumin (0–0.2% w/v) within artificial urine, the concentration of magnesium chloride hexahydrate (0–0.36% w/v) and the presence or absence of urease on the mass of calcium and magnesium encrustation on the selected biomaterials. The pH values of the various artificial urine solutions were monitored potentiometrically. Finally, in order to examine the effects of various urease inhibitors on encrustation on the various biomaterials, methylurea, ethylurea or acetohydroxamic acid (each 10 mM) were incorporated into the standard artificial urine and the mass of calcium and magnesium encrustation determined following immersion within the encrustation model for 1 week. This model exhibited high reproducibility, attributed to improved stirring conditions (since the entire vessel is placed on a gyrorotary platform), and also demonstrated the potential for reducing urinary encrustation by incorporation of agents that modify urease activity, such as acetohydroxamic acid, into biomaterials.

3.5. Static encrustation vessel containing five stent sections.

Figure reproduced from reference 60 with permission from Wiley Periodicals Inc.

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Dropping Acid and Heavy Metal Reactions

Daniel A. Vallero Ph.D., in Paradigms Lost, 2006

Acid Precipitation

Eastern and midwestern coals contain significant quantities of sulfur, so burning them releases large quantities of sulfur dioxide (SO2), the major component of acid precipitation, to the atmosphere. Most of the high-sulfur coal consumed in the United States during this century has been used to make steel and to generate electricity in the East and Midwest. From there, atmospheric pollutants responsible for acid precipitation are transported northward and eastward by prevailing winds and storms. These trends are reflected in the geographic distribution of rainfall pH (see Figure 8.4). Emissions from coal-fired electric generating plants presently constitute the largest source of atmospheric SO2. Other constituents of acid precipitation, including those from automotive exhausts, are distributed similarly.

FIGURE 8.4. United States rainfall pH, 2003, as weighted mean values based on measurements at about 200 sites maintained by the National Acid Deposition Program.

Source: National Acid Deposition Program/National Trends Network; http://nadp.sws.uiuc.edu/isopleths/maps2003/phfield.gif, accessed on August 23, 2005.

Areas with underlying crystalline rock, shale, and sandstone are more prone to acidification than those underlain by rock systems that buffer the acids, such as limestone and other carbonate-rich rock. Potentially sensitive areas are widely distributed in North America and include much of the Appalachian Mountains, where rainfall is most acidic (see Figure 8.4); the Canadian Shield region of the upper Midwest (that is, the northern parts of Michigan and Wisconsin, as well as eastern Minnesota and parts of eastern and central Canada); the higher elevations of the Sierra Nevada, Rocky Mountains, and Cascade Range; and parts of the Ozark and Ouachita uplands, mid-Atlantic Coastal Plain, and Florida. Buffering by ions in ground water and constituents leached from watersheds makes large lakes and rivers at lower elevations less susceptible to acidification than smaller, higher-elevation lakes and streams.

The interactions of ions in precipitation (i.e., H+, SO4+2, NO3−2) with organic and inorganic constituents of soil and water affect toxicity. Particularly important is the leaching of potentially toxic elements, especially aluminum, from rocks and soils by acidic precipitation. Toxicity attributable to pH and aluminum is often episodic, occurring during high surface-water discharge in the spring months. Spring is also the time when spawning and larvae releases occur for many aquatic organisms, making them vulnerable to reduced pH conditions.

By definition, acid rain is rainfall with a pH lower than about 5.0; the pH of distilled water in equilibrium with atmospheric CO2 is 5.6, but other atmospheric constituents tend to make rainfall more acidic even in areas unaffected by air pollution. In addition to sulfur, the combustion of coal emits other potentially toxic elements, including arsenic, cadmium, lead, mercury, and selenium. Cadmium and selenium are concentrated in coal ash, from which they may be leached into surface waters and accumulated to toxic concentrations by aquatic organisms. Mercury, along with selenium and other elements in coal are released into the atmosphere in stack emissions and can move long distances. Mercury and selenium readily bioaccumulate in birds, mammals, and predatory fishes. Mercury is generally released from point sources (e.g., caustic soda, that is, sodium hydroxide (NaOH) plants and paper mills). Bioaccumulation of mercury in remote lakes in the Northeast seems to indicate that atmospheric transport and natural chemical processes tend to keep mercury available for accumulation by organisms. According to the U.S. EPA, coal-fired electric generating plants are the greatest sources of atmospheric mercury; other important sources include municipal and hospital waste incinerators.

Metals are the elements listed on the left side of the periodic table of elements (see Figure 8.5). They form positive ions (cations), are reducing agents, have low electron affinities, and have positive valences (oxidation numbers). Nonmetals, listed on the right side of the periodic table, form negative ions (anions), are oxidizing agents, have high electron affinities, and have negative valences. Metalloids have properties of both metals and nonmetals, but two environmentally important metalloids, arsenic (As) and antimony (Sb), behave much like metals in terms of their toxicity and mobility, so they are often grouped with the heavy metals.

FIGURE 8.5. Periodic table of elements.

For most metals, the chemical form determines just how toxic it is. The form also determines how readily the metal moves in the environment and how rapidly it is taken up and stored by organisms. The chemical form is determined by the oxidation state or valence of the metal.

At some concentration, every element except those generated artificially by fission in nuclear reactors are found in nature, especially in soils. Thus, it would be absurd to address metal contamination problems by trying to "eliminate" them. This is a common misconception, especially with regard to heavy metal and metalloid contamination. For example, mercury (Hg) and lead (Pb) are known to be important contaminants that cause neurotoxic and other human health effects and environmental pollution. The global mass balance of these metals, however, does not change; only the location and form (i.e., chemical species) can be changed. Therefore, protecting health and ecological resources is a matter of reducing and eliminating exposures and changing the form of the compounds of these elements to render them less mobile and less toxic. The first place to start such a strategy is to consider the oxidation states, or valence, of elements (see Chapter 2).

Let us consider two metals, one metalloid, and a mineral fiber known to cause environmental problems.

4.3 Acid Rain

Acid rain is the name given to any precipitation from the atmosphere that is abnormally acidic in nature. The term became common currency during the 1980s when the adverse effects of acidic precipitation on the environment first caused major concern. At its worst, acid rain can affect fish populations, cause degradation and even death of lakes and streams; it causes erosion on buildings and is hazardous to human health. Recognition of this eventually led to the control of the emissions responsible for the acidification.

The effect known as acid rain was first identified in Sweden in 1872, but it was not until the 1970s, again in Scandinavia, that the modern effects were clearly identified. Since then it has been studied in many parts of the world and its impact quantified. The acidity of water is classified according to its pH, a logarithmic scale of the hydrogen ion concentration. Neutral water has a pH of 7; below that is considered acid and above is alkaline. Normal rain absorbs carbon dioxide from the atmosphere, forming carbonic acid that is slightly acidic, so that the normal pH of rain is 5.6. Acid rain has a typical pH of between 4.2 and 4.4.

Higher acidification of rain is caused by the presence of sulfur dioxide or nitrogen oxides in the atmosphere. When these are absorbed by moisture in the atmosphere, they can form sulfuric acid or nitric acid, much more potent acids that carbonic acid, and these can lead to much higher levels of acidity. The effect is illustrated diagrammatically in Fig. 4.1. The level of acidity is critical for some species. For example, below a pH of 5, fish eggs cannot hatch while for frogs the critical pH is 4. Elsewhere acidic precipitation leads to dying of trees.

Figure 4.1. Acid rain.

Modified version of Wikipedia image.

There are a number of natural sources of acid rain. These include sulfur dioxide released from volcanic eruptions and nitrogen oxides generated by lightning. However, the main sources of the acidic gases in the atmosphere are from human activity. The electric power industry probably makes the biggest contribution, accounting for two-thirds of sulfur dioxide in the atmosphere and around one quarter of the nitrogen oxides.

Acid rain can arrive at the surface of the earth as either wet or dry deposition. Wet deposition, in the form of rain, snow, fog, and hail, is what the term acid rain normally brings to mind. However, it can also fall as acidic gases and particles that are deposited directly from the atmosphere. These particles can be harmful to human health if inhaled. Dry acidic deposition will be washed off during the next rainfall, draining into the soil, rivers, and streams where it will cause damage in the same way as wet deposition.

The flue gases from power plants, carrying any acidic gases, are normally swept high into the atmosphere. Winds can then carry the gases over long distances before they are deposited again. In consequence, acid rain can be transported from nation to nation and region to region. Acidification of lakes in Scandinavia, for example, has been linked to emissions of sulfur dioxide in the United Kingdom. In the United States trans-state acid rain transportation has been common. Long distance transport makes acid rain a global problem.

Acid rain has been linked to a number of specific problems:

Forests: Acidic rain leeches aluminum from the soil. This is often harmful to plants and animals and is thought to be one of the main causes of the death of trees, which is common in forests affected by acid rain. The acidic rainwater may also strip essential nutrients from the soil, again harming plants and trees that rely on them. At high altitudes, trees may be exposed to fogs and clouds of acid rain, which strip nutrients directly from leaves, weakening them and making them less able to carry out photosynthesis. It may also reduce their resistance to freezing and to disease. Some soils, which are naturally alkaline, may buffer the acidic influence, in which case they can be resistant to the effects.

Streams, rivers, and lakes: Waterways including streams, rivers, and lakes are particularly vulnerable to the effects of acid rain. When the acidity of a steam or lake falls below that of natural rainwater, 5.6, many species struggle. A few fish can survive below pH 5 and if the pH falls as low as 4, most life will have been lost and a lake will be considered dead. In between, most species will die but a few acid-tolerant species may survive. However, this is likely to skew the ecology of the system dramatically. As with soils, not all lakes and waterways are vulnerable. Those on alkaline soils and rocks can buffer the acidity and resist its effects.

Plants and crops: Crops and plants will be affected in exactly the same way as trees and forests if acid rain removes nutrients for soils or leeches aluminum, which can damage their growth. Typical effects include stunted growth.

Buildings and man-made structures: Acid rain can both cause and accelerate the corrosion and destruction of many building materials including stone and metal. Much of the erosion and damage to city structures during the 20th century may be linked to acid rain. Some of the materials used to construct older or ancient buildings have proved to be the most vulnerable, and major monuments such as the Taj Mahal in India, Cologne Cathedral in Germany, the Colosseum in Italy, and Westminster Abbey in the United Kingdom have all suffered material damage as a result of acid rain.

Human health: Acid rain can be injurious to human health if inhaled directly. The most serious widespread problem is from acidic fog that can cause respiratory problems if inhaled. People with asthma or those who are already weak are particularly vulnerable.

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Overview of the Chemistry of Polluted and Remote Atmospheres

Barbara J. Finlayson-Pitts, James N. PittsJr., in Chemistry of the Upper and Lower Atmosphere, 2000

b Overview of Acidic Rain and Fogs

Acid rain arises from the oxidation of SO2 and NO2 in the troposphere to form sulfuric and nitric acids, as well as other species, which are subsequently deposited at the earth's surface, either in precipitation (wet deposition) or in dry form (dry deposition). The contribution of organic acids has also been recognized recently (see Chapter 8). These oxidation and deposition processes can occur over relatively short distances from the primary pollutant sources or at distances of a 1000 km or more. Thus both short-range and long-range transport must be considered.

The gas-phase oxidation of both SO2 and NO2 is initiated by reaction with hydroxyl radicals:

(28)OH+SO2 M→ HOSO2→H2o→ H2SO4,

(10)OH+NO2 M→ HNO3.

In the case of SO2, oxidation in the aqueous phase, present in the atmosphere in the form of aerosol particles, clouds, and fogs, is also important. Thus SO2 from the gas phase dissolves in these water droplets and may be oxidized within the droplet by such species as H2O2, O3, O2, and free radicals. Oxidation of SO2 on the surfaces of solids either present in the air or suspended in the water droplets is also possible. On the other hand, it is believed that HNO3 is formed primarily by reaction (10) in the gas phase and subsequently dissolves in droplets.

These oxidation processes can lead to highly acidic fogs. For example, pH values as low as 1.69 have been measured in coastal regions of southern California (Jacob and Hoffmann, 1983). These high acidities, accompanied by high concentrations of other anions and cations, are likely due to evaporation of water from the fog droplets, leaving very high concentrations of ions in a strongly acidic liquid phase. Such acid fogs, whether in London or Los Angeles, are a major health concern because the droplets are sufficiently small to be efficiently inhaled (Hoffmann, 1984).

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Environmental Disasters

Mukesh Doble, Anil Kumar, in Biotreatment of Industrial Effluents, 2005

Various Disasters

This chapter briefly describes the various disasters that have occurred in the past few years and the problems caused by them. The study of various incidents should help us to develop manufacturing processes that do not pollute, evolve safe means of disposing of toxic effluents, and avoid the hazards involved in storing and transporting toxic materials.

Acid Rain

Acid rain is rain with a pH of less than 5.7, which results from high levels of atmospheric nitric and sulfuric acids that get washed down to earth. Oxidation of sulfur and nitrogen in coal or other fossil fuels leads to the generation of acidic pollutants in the atmosphere. Acid rain has caused considerable damage to forests in many developed countries. Use of low-sulfur coal and gasoline can prevent acid rain.

Carbon Dioxide

CO2 is not a pollutant in the conventional sense, since it is essential for plant growth. Combustion of fossil fuels, including coal-fired thermal power stations and forest fires, has increased the background levels of CO2 from 315 ppm in 1960 to 405 ppm in 2000, which leads to an atmospheric greenhouse effect, which in turn increases the average temperature.

Ozone Layer Depletion and Human Health

In 1993 the atmospheric ozone layer surrounding the earth thinned to the lowest levels ever recorded. With the loss of stratospheric ozone, the atmosphere became more transparent to radiation, resulting in an increase in the amount of ultraviolet (UV) solar radiation reaching the earth. It has been found that an increase in UV radiation can lead to an increase in human diseases, including skin cancers, eye damage, and reduction in the effectiveness of the body's immune system. White skin is more prone to burning than black or brown skin. The Arctic ozone holes within the next 10 to 20 years could affect inhabited areas of northern Europe, Canada, and Russia (New Scientist, Oct. 10, 2000).

The ozone layer is affected because of emissions from earth and deposition in the stratosphere of compounds such as bromofluorocarbons (halons), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), CO2, nitrogen oxides (NOX), chlorinated carbons, methyl bromide (CH3Br), methane (CH4), and nitrous oxide (N2O). CFCs are among the most important ozone-depleting substances; they are used in aerosol propellants, coolant agents in refrigerators, cleaning agents, and plastic foam-blowing agents. An international agreement was reached (the Montreal Protocol and its amendments, signed by 148 countries) that banned the production of most CFCs by the year 2000, and the Copenhagen amendment to the Montreal Protocol called for the cessation of HCFC (an alternate to CFCs) production by 2030.

Global Warming — Petrol versus Diesel

Based on some theoretical studies, it is believed that CO2 produced by petrol engines could be less harmful to the planet than the soot and dust produced by diesel engines. A climate model showed that the soot produced by diesel engines will warm the climate more over the next century than the extra CO2 emitted by petrol-powered vehicles. In addition, the soot particles would alter the humidity of air by allowing water droplets to condense around them, causing pollutants to accumulate in the air and change weather patterns. Hence 1 g of black carbon is 360,000 to 840,000 times as powerful a global warming agent as 1 g of CO2.

Pollution Reducing Sunshine

Airborne pollutants have led to a steady decline in sunshine in vast polluted regions of eastern China. The amount of sunshine has fallen by between 2 and 3% a decade, and the maximum summer temperatures have also fallen by around 0.6°C a decade. In Zambia and the Brazilian Amazon, pollution blots out around a fifth of the sun's radiation at certain times of year (Freeman, 1990; New Scientist, 2002e).

Polychlorinated Biphenyls in the Environment

About 80 million pounds of polychlorinated biphenyls (PCB) are produced annually, and they find applications in capacitors, transformer oils, and heat transfer fluids. Half the amount is used as plasticizers, hydraulic fluid, and adhesives, as well as in carbon paper. About 10 million pounds escape annually and become environmental contaminants. These are very stable compounds, do not degrade, and accumulate in animal tissues. PCBs have been found in polar bears in the Arctic and penguins in Antarctica, creating havoc. Killer whales in the Gulf of Alaska are among the most heavily PCB-laden marine mammals in the world, and their numbers are in rapid decline.

Methyl Tertiary Butyl Ether (MTBE)

MTBE is an "oxygenate" that makes gasoline burn cleaner and more efficiently, but it is also identified as a probable carcinogen that spreads rapidly when gasoline escapes from leaky underground storage tanks, contaminating sources of groundwater and drinking water from New York to California in the United States. At least 16 states already have passed measures to ban or significantly limit the use of MTBE in gasoline.

Exxon Valdez Spill

The grounding of the oil tanker Exxon Valdez on Bligh Reef on March 24, 1989, released almost 11 million U.S. gallons of North Slope crude oil into the waters of Prince William Sound, Alaska. A major storm a few days later spread the oil into the shorelines of the numerous islands in the western part of the Sound and out into the Gulf of Alaska. Bioremediation was carried out by the application of an oleophilic liquid fertilizer, a micro emulsion of a saturated solution of urea in oleic acid containing tri(laureth-4)-phosphate and butoxy-ethanol to stimulate the activity of the oil-degrading bacteria. Two weeks after application of the fertilizer, the cobbles on the treated section of the shoreline were substantially clean. But most seabird populations hit by the oil spill have not shown signs of recovery even a decade after the disaster (New Scientist, May 2001).

Pipeline spills reported to the U.S. Department of Transportation average 12 million gallons of petroleum products a year. The U.S. General Accounting Office says an average of 16,000 small oil spills seep into waterways each year, half of them during loading or unloading operations, and the real number could be three to four times that.

Cyanide Spill at Baia Mare, March 2000

On January 30, 2000, following a breach in the tailing dam of the Aurul SA Baia Mare Company, a major spill of cyanide-rich tailings waste from the extraction of precious metals was released into the river system near Baia Mare in northwest Romania. The contaminant traveled via tributaries into the Somes, Tisza, and finally the Danube rivers before reaching the Black Sea (UNEP/OCHA Environment Unit, 2000).

Corals Affected by Human Waste

Human wastewater containing undegraded drugs and antibiotics is having a bad effect on the aquatic environment, especially on the corals off the coast of Florida, which form the world's third largest barrier reef (New Scientist, 2002b). It has been found that half of the live coral off the Florida coast has disappeared in the past 5 years. The fish that feed on these corals have developed deformities and died in much higher numbers than usual.

Movement of Pollutants into Coastal Aquifers

Wells located near coasts could be more polluted than the ones located inland because the pollutants dumped into the sea diffuse faster through the soil barrier (they are less soluble in salty water because of the "salting out effect") (New Scientist, 2003b). This phenomenon can be observed in the movement of pollutants from sea to the coastal aquifers — natural reservoirs of freshwater held in porous rock and also toward coastal agricultural land.

Chernobyl Accident

The Chernobyl accident in the Ukraine in 1986 was the result of a flawed nuclear reactor design. The reactor was operated with inadequately trained personnel and without proper regard for safety, leading to a steam explosion and fire that released ∼5% of the radioactive reactor core into the atmosphere and downwind of the plant. Some 31 people were killed, and there have since been around 10 deaths from thyroid cancer attributed to the accident.

Bhopal Disaster

On December 2, 1981, more than 40 tonnes of methyl isocyanine (MIC) and other lethal gases, including hydrogen cyanide, leaked from a pesticide factory at the northern end of the Bhopal, the capital of Madhya Pradesh, India. More than 8,000 people were killed, and more than 500,000 people suffered multisystemic injuries. Toxic gas exposure was found to have had a detrimental effect on the immune system (Lepkowski, 1985).

Bashkiria Train–Gas Pipeline Disaster

The Bashkir train–gas pipeline disaster occurred in June 1989. At least 400 people were killed when a pipeline transporting a methane-propane mixture exploded as two trains were passing, causing 400 immediate deaths and more than 800 casualties, mostly with burns (Kulyapin et al., 1990).

Seveso Dioxin Accident

Dioxins and furans are halogenated aromatic hydrocarbons that are commonly produced by combustion of fossil fuels and incineration of municipal waste, as a byproduct of pulp and paper bleaching, and in the production of other chemicals. 2,3,7,8-Tetrachlorodibenzo-p-dioxin is the most toxic member of this family. It is an endocrine disrupter as well as a potent animal carcinogen and teratogen that persists in both the environment and biological tissues. On July 10, 1976, a valve broke at the Industrie Chimiche Meda Societa Azionaria chemical plant in Meda, Italy, releasing about 3,000 kg of dioxin-containing chemicals into the atmosphere. Approximately 4% of local farm animals died, and roughly 80,000 animals were killed to prevent the contamination from moving up the food chain. It is believed that this exposure affected the sex ratio in future progeny.

Czech Plant Leaked Hundreds of Kilos of Deadly Gas

Several hundred kilograms of highly poisonous chlorine gas leaked into the air in an accident at a flooded chemical plant in the Czech Republic on August 23, 2002. The accident happened when workers at Spolana, a unit of the chemicals group Unipetrol, pumped fluid chlorine gas out of a storage unit that had been damaged in the flood. There were no casualties in the accident.

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Health, Safety and Environmental Issues

M.N. Bassim, in Comprehensive Materials Processing, 2014

8.11.3.1.2 Acid Rain

The phenomenon of acid rain occurs when the rain, ordinarily consisting of water which is neutral with a pH of 7.00, becomes acidic, with the pH dropping below the generally acceptable value of 5.2 and perhaps going as low at 2.5 in industrialized areas. As with other manifestations of impact of manufacturing and industrialization impact, acid rain was known and observed as early as the eighteenth century in some parts of England. It was not, however, considered a danger to the environment because in the early years of the Industrial Revolution it was a rare occurrence.

With increased awareness of the health and environmental effects of manufacturing, following World War II, due in large part to a significant increase in manufacturing activities in the industrialized countries and to other parts of the world, the problem of acid rain became a serious environmental issue. Ongoing studies to prevent acid rain and to eliminate its negative effects on the aquatic life are underway.

The main source of acid is the burning of coal in order to operate power plants that produce electricity. Coal containing sulfur produces sulfur dioxide gas (SO2) as coal is burned and forms sulfuric acid when it reacts with water vapor in clouds. Other gases that can be produced are nitrogen oxides that react with water to form nitric acid.

Complex chemical reactions in the atmosphere eventually led to the formation of acid rain. Acid rain is truly a global phenomenon and occurs in many parts of the world. Its incidence is more likely in higher altitude areas such as mountains and the forests that grow on mountain slopes, and may occur thousands of kilometers (miles) away from coal-burning sites when downwinds carry the smokestack fumes for long distances.

It is generally estimated that up to 10% of lakes have a higher concentration of acidic ions than what is considered to be safe for aquatic life. Acid rain is generally not harmful to humans because of the weak concentration of acids, but it does have a strong impact on the aquatic life in lakes, rivers, and streams. Acid rain produces the premature death of fish living in these waters or may cause changes in the life cycles, in terms of spawning and reproduction of fish species. Acid rain also has an adverse effect on arable soils since it changes the chemistry of the soil and renders it less efficient for agriculture. Its effect is also felt on naturally growing forests, particularly those at high elevations on mountainsides. Acid rain is also known to affect monuments and historical buildings built with limestone, which react with the acid and crumble with time. This particular effect has created a worldwide effort, and treaties have been negotiated to protect these historical statues and monuments from the negative effects of acid rain.

A concerted effort has been made to produce and use clean burning coal in electricity-producing power plants isolating sulfur before burning. Car emissions, also a source of acidic gases, have been regulated, and their occurrence is limited by catalytic converters, which have reduced these emissions considerably.

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Nitrogen Cycle, Atmospheric

Dan Jaffe, in Encyclopedia of Physical Science and Technology (Third Edition), 2003

II.C.2 Acid Rain

Acid precipitation, or acid rain, can causes significant impacts on freshwater, coastal, and forested ecosystems. Both NO3− (from NOx emissions) and SO42− (from SO2 emissions) contribute significantly to acid rain. The relative ratio of SO42− / NO3− in precipitation will be substantially determined by the regional emissions of SO2 and NOx. In regions that get most of their energy from coal and other high-sulfur fuels, there will be significant emissions of SO2 unless scrubber technology is employed. Due to declining emissions of SO2 in developed regions of the world and increasing NOx emissions, from automobiles, the relative contribution of NO3− is changing, with NO3− contributing an increasing fraction of the acidity in acid rain. In ice cores collected in remote regions of the northern hemisphere, SO42− and NO3− concentrations have increased significantly in the past 50 years, reflecting the large increase in source emissions due to anthropogenic sources.

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Current Heterogeneous Catalytic Processes for Environmental Remediation of Air, Water, and Soil

Vasile I. Parvulescu, Pascal Granger, in New and Future Developments in Catalysis, 2013

17.2.4 DeSOx Purification

SO2 is responsible for acid rains and its abatement is a major environmental problem [76]. The level of SO2 emission is still very high and the solution actually recommended is still not efficient. China and India are the two largest anthropogenic aerosol generating countries in the world [77]. These emissions result mostly from the combustion of coal, fluid catalytic cracking units and synthesis of sulfuric acid plants are generally accompanied by the economic development. The 46% increased emissions in these two countries in the last decade are, thus, very good evidence.

Most of the studies devoted to the removal of SO2 refer to its adsorption on different adsorbents. To date, the least costly means is the use of a so-called sulfur-transfer technique, which consists of mixing a catalyst with a sulfur-transfer agent [78,79]. The sulfur-transfer agent can fix SOx as sulfate species under an oxidizing atmosphere.

Hydrotalcite-based mixed oxides and spinels with different compositions [80–82] have already shown their efficiency in such reactions. Some rare-earth metal oxides and/or transition metal oxides are usually introduced into the spinel structures in order to improve the De-SOx activity.

Multimetallic layered double hydroxides in which ceria was incorporated in different amounts as oxidation promoter are examples of precursors for such catalytic systems [83]. Microsphere particles with mechanical properties that are adequate for fluidization prepared following this approach were evaluated in a pilot-scale fluid catalytic cracking plant, appearing as a viable, low investment, flexible, and effective option for in situ reduction of SOx flue gas emissions.

Simultaneous removal of sulfur dioxide and nitrogen dioxide has also been investigated with other absorbents, like those made of Al2O3 impregnated with alkaline basic species [84] or with zirconium hydroxide [85].

Bare and Pt-containing CeO2 were identified as potential regenerable sulfur oxide traps [86]. The samples were evaluated by lean SOx adsorption where the presence of Pt was found to enhance the lean SOx storage capacity for CeO2-based samples. Lean SO2 adsorption was found to proceed via the formation of surface and bulk sulfates. In the presence of a strong oxidant, MnO2 in a pyrolusite slurry can also oxidize SO2 and NO2 into MnSO4 and Mn(NO3)2 with a high SO2 removal efficiency [87].

The oxidation of SO2 to SO3 resulting in sulfuric acid manufacture is another attractive approach. Most of the flue gases from metallurgical plants contain SO2. The main difficulty for achieving high conversions is the low SO2 content in these gases (<3%). This is critical since the reactor in the contact process operates in an autothermal regime, so the amount of heat generated depends on the SO2 content in the feed. In the case of dilute gases the evolved heat is not enough to satisfactorily activate the desired reaction. The catalyst is a key factor in this process, and the use of mesoporous catalysts demonstrated a bifunctional behavior: SO2 is concentrated by the mesoporous support followed by its oxidation by molten salt complexes [88–90]. Operando Raman measurements with these catalysts show that the deposition of Cs2SO4 onto mesoporous silica-vanadia supports prepared by sol-gel methods led to a mononuclear VVO2(SO4)23− molten oxosulfato complex, which during the activation with SO2 generated an active binuclear (VVO)2O(SO4)44− molten oxosulfato complex [91]. A fairly good correlation between the surface areas of V2O5/SiO2 precursors and TOF values was found for the resultant V2O5–Cs2SO4/SiO2 molten salt catalysts. SO2 oxidation in feed gases with low SO2 content, i.e., less than 2%, occurred with almost complete conversions.

The use of a SOx-reduction catalyst is a known route to recovery of sulfur from refinery plants following the Claus concept. Supported vanadia catalysts, such as the Amoco DeSOx catalyst (V2O5/CeO2/Mg2Al2O5), confirmed the efficiency of the concept [92].

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Environmental Geochemistry

S.A. Norton, ... I.J. Fernandez, in Treatise on Geochemistry (Second Edition), 2014

11.10.6.2 Nutrient Availability

The initial response to acid rain is an increase in the mobilization and export of base cations and, commonly, SO4 and NO3 from the watershed. In general, soil acidification and associated leaching of Mg, Ca, and K, and elevated Al mobilization are usually associated with less favorable nutritional status, whereas N deposition tends to increase the fertility of naturally N-limited terrestrial ecosystems (Puhe and Ulrich, 2001). The elevated N deposition thus may correspond to a period of fertilization of plants in forests and in N-limited surface waters. However, prolonged increased leaching of exchangeable base cations and subsequent decline in exchangeable pools of base cations in soils (Fernandez et al., 2003; Kirchner, 1992; Likens et al., 1996) can have a long-term impact on terrestrial ecosystem health. As the molar ratio (Ca + Mg + K)/Al in soil solution declines during acidification, nutrient uptake by roots can be impaired. Limited Ca or Mg uptake, associated with elevated Al concentrations and low pH in the rooting zone, slows growth and decreases the stress tolerance of trees (Cronan and Grigal, 1995), and adversely affects tree physiology (Šantrůčková et al., 2007). Declining Ca in runoff, which may occur during acidification or recovery, has been implicated in reduced fecundity and survival of Ca-rich Daphnia species (Jeziorski et al., 2008). Similar effects might be expected in other organisms that require higher Ca in water.

Although P is not commonly the subject of acid rain geochemistry research, ecosystem alterations due to acidification inevitably alter P dynamics in watersheds. Reinhardt et al. (2004) demonstrated that the export of P in runoff from the experimentally acidified catchment at BBWM had increased nearly by a factor of 10, along with Al. SanClements et al. (2010) reported that an important source of this P and Al was in the B horizon of these forested Spodosols, a locus of secondary Al and Fe accumulation and thus, significant P adsorption capacity. They suggested that mobilization of Al by the experimental acidification also resulted in P mobilization, and that this effect was evident at both BBWM and a similar experimental watershed acidification study at the Fernow Watershed in West Virginia, USA. Evidence also existed to suggest that for the period of time of accelerated P mobilization, which could be transient, P was more available to biota, with biocycling of this P resulting in redistributions within the ecosystem.

Minimally polluted forest ecosystems export mostly organically bound N and NH4, instead of inorganic oxidized N (NO3) (e.g., Hedin et al., 1995; Perakis and Hedin, 2002). Increased atmospheric deposition of N can initially have a positive growth effect on N-limited ecosystems. Turnover of mineralized N in the forest floor is generally an order of magnitude higher than atmospheric input of inorganic N, which creates only a small addition to a large N soil pool. Nitrogen demands by biota must be satisfied first, and a certain amount of N can be immobilized in forest organic matter, before N saturation and chronic NO3 leaching occur (Aber et al., 1989, 1998; Stoddard et al., 2001). Ecosystems vary widely in their capacity to retain N inputs. Excess N is exported mostly as NO3, increasing the concentration of SAA in water, contributing to acidification. Nitrate leakage is greatest from high-elevation, steep sites, and from mature forests with high soil N stores and low soil C/N ratio (Fenn et al., 1998), and lowest from watersheds containing extensive wetlands. Concentrations and seasonality of NO3 in stream water are used as indices of N saturation (Stoddard, 1994). Mosello et al. (2000) and Kopáček et al. (2001a) indicated that retention of N in watersheds decreased with time under acidification stress. In contrast, slightly elevated terrestrial N retention may be connected to reduction of acidic deposition during the recovery phase (Lorz et al., 2002; Veselý et al., 1998a, 2002a). Increased concentration of NO3 in streams increases P demand and the risk of P limitation in stream microbial communities, as demonstrated at BBWM (Simon et al., 2010). This P limitation can be exacerbated by the mobilization of Al from soils and subsequent precipitation of Al(OH)3 in streams, increasing the capacity for adsorption of dissolved P. Davison et al. (1995) used whole-lake treatment with P to overcome acidification by excess NO3.

Export of NO3 in surface waters is linked to soil microbial activity and the soil C/N ratio (Yoh, 2001). Empirical data showed that a C/N ratio of the forest floor <25 and throughfall deposition above 9–10 kg N ha−1 year−1 were thresholds for leaching NO3 in Europe (Dise and Wright, 1995; Gundersen et al., 1998), with similar findings reported for North America (Aber et al., 2003). In the European data, the slope of the relationship between N input and NO3 leached was twice for sites where C/N < 25. Higher rates of NO3 leaching also occurred at sites with pH < 4.5 and high N input (MacDonald et al., 2002). However, N leakage was about half that of deposition at high-elevation alpine sites in the Rocky Mountains of Colorado, USA (Williams et al., 1996). The export of NO3 from N-saturated forests also reflects the soil's potential for nitrification and land-use history. Goodale and Aber (2001) reported that although net N mineralization did not vary by land-use history, nitrification rates doubled at old-growth sites compared to younger hardwood forests disturbed by fire and harvesting about a century ago. Enhanced nitrification at old-growth sites could have resulted from excess N accumulation relative to C accumulation in soils. Carbon mineralization rates and C/N ratios were comparable in spruce forest soils for two neighboring watersheds in the Bohemian Forest, Czech Republic, while potential net N mineralization and nitrification differed by 50–70%; higher potentials were associated with higher leaching of NO3 (Kopáček et al., 2002a). In Europe, as SO4 deposition and runoff SO4 has declined, NO3 has become the major anion in some surface waters. Nitrate thus dominates the acidification status of these systems, as well as being the most important driver of episodic acidification and Al mobility (Kopáček et al., 2009).

The productivity of temperate freshwaterlakes and streams is generally limited by the availability of phosphorus, although light limitation can be of primary importance in already P-poor lakes (Karlsson et al., 2009). Phosphorus occurs in many rocks, primarily in the mineral apatite, which has a relatively high weathering rate. Consequently, older soil profiles are depleted in apatite. Monazite ((REE)PO4) is common in many rocks but the mineral is very insoluble. Much P is concentrated in organic-rich soils and is strongly recycled or sequestered by adsorption in Al- and Fe-rich illuvial soil layers (SanClements et al., 2009). Lakes predisposed to acidification thus have low concentrations of base cations and P. Acidification of catchments can result in a slightly increased export of dissolved P from soils (Roy et al., 1999). Roy et al. (1999) and Reinhardt et al. (2004) found that two contiguous acidifying streams contained high concentrations of particulate acid-soluble Al and Fe hydroxides and acid-soluble particulate P during acidic episodes. Particulate P was 10–50 times higher than dissolved P and highest in the lower pH stream. Ionic Al species hydrolyze downstream or in lakes at higher pH, as polymeric Al species are formed with large specific surfaces and with strong affinity for PO43−. The P in acidified streams and lakes (typically with a pH in the 5.5–6.5 range) can be scavenged by these Al- or Fe-rich particles. If the Al hydroxide is deposited as sediment, the flux of P into sediment can be irreversible (Kopáček et al., 2001b), even during periods of hypolimnetic anoxia when pH typically increases, Fe hydroxide dissolves, and adsorbed P would normally be released to the water column (Amirbahman et al., 2003; Einsele, 1936). Thus, stream acidification can lead to downstream oligotrophication as suggested by Dickson (1978).

As DOC has increased during the decline of SO4 in runoff, the mobilization of Al to lakes should have increased because Al–DOC complexes, regardless of pH trend. Kopáček et al. (2000, 2005) have demonstrated that precipitation of Al(OH)3 in the water column of Plešné Lake, Czech Republic, removes P from the lake P-cycle, thereby lowering biologically available P. The source of the Al is partly from inorganic mobilization because of acidification and dominantly from complexation with soil DOC, followed by Al liberation due to photooxidation of the complex in the lake water column. If Al partially controls bioavailability of P, then there is likely a linkage between P and Hg in fish. Higher dissolved P in a lake enhances the food chain, thereby diluting the Hg concentration in algae and the subsequent food chain, including fish. Conversely, if P is lowered in the water column, productivity is reduced and Hg concentration will be higher in the food chain, particularly fish. This concept of biodilution (Chen and Folt, 2005) is not fully understood but is a pressing problem.

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Wood: Finishes and Coatings

W.C. Feist, A.A Abdullahi, in Reference Module in Materials Science and Materials Engineering, 2016

5 Acidic Deposition

The attention given to acid deposition (acid rain) during the 1990s prompted interest in the effect of acids on wood finish durability and on wood weathering (Williams, 1991). It has been shown that in the summer, the decisive factor in wood weathering is the intensity of solar radiation, whereas in the winter, it is the increased amount of sulfur dioxide in the surrounding air (central Europe exposure). The effects of acid rain on painted materials can be seen in the degradation of the coating and substrate. The type of pigment and extenders used in paint formulations has a direct bearing on paint performance in an acid environment. The degradation of the substrate also has a direct bearing on coating performance, and may induce different coating failure mechanisms.

Studies in Environmental Science

Volume 25, 1984, Pages 233-259

Acid Precipitation: A Review

Author links open overlay panelU.M.Cowgill

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https://doi.org/10.1016/S0166-1116(08)72112-5Get rights and content

Abstract

There are two major groups of thought concerning acid precipitation. Group I holds the view that this environmental problem requires legislative attention, that such precipitation results chiefly from the combustion of fossil fuels which releases oxides of N and S into the atmosphere. Once present N and S may undergo transformation to their respective acids and these substances may be transported great distances. Once deposited, these acids cause damage not only to all components of the natural landscape, but also to statues, monuments, buildings and other anthropogenic materials. In addition, this group opines that this phenomenon has persisted since the mid–1950s; that the problem has worsened and the area affected is steadily expanding. Proponents of Group I present data illustrating a mean decline of 0.5 pH units below the norm for rain (pH 5.6) in the regions affected.

The Group II offers several alternative explanations for the reported and sometimes observed phenomena. They suggest that acid conditions noted in water bodies result from drastic changes in land use, that reexamination of historical data reveal these data to be trendless, that local and natural sources of N and S oxides, especially resulting from the combustion of oil, play a major role in the formation of acidic precipitations in the region at risk. Finally, Group II points out that it is difficult to quantitatively attribute the phenomenon of acid rain falling in one place to its origin in another place.

This review discusses meteorological, physical and biological aspects of acid precipitation from the two points of view just presented and emphasizes the known and the unknown in this complicated area of research.

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