🗊Презентация Acidification in the Arctic

Acidification in the Arctic

General Question about Acidification Аcid deposition occurs when sulfuric acid, nitric acid, or hydrochloric acid, emitted into or produced in the air as a gas or liquid, deposits to soils, lakes, farmland, forests, or buildings. Deposition of acid gases is dry acid deposition, and deposition of acid liquids is wet acid deposition. Wet acid deposition can be through rain (acid rain), fog (acid fog), or aerosol particles (acid haze).

General Question about Acidification Acid deposition is caused by the emission or atmospheric formation of gas- or aqueous-phase sulfuric acid (H2SO4), nitric acid (HNO3), or hydrochloric acid (HCl).

History of the problem Historically, coal was the first and largest source of anthropogenically produced atmospheric acids. During the Industrial Revolution, which started in the eighteenth century, coal was used to provide energy for the steam engine. In the late eighteenth century, a second major source of atmospheric acids emerged. Around 1780, the demand for sodium carbonate [Na2CO3(s)] (also known as soda ash, washing soda, and salt cake), used in the production of soaps, detergents, cleansers, glass, paper, bleaches, and dyes, increased

History of the problem Method of producing soda ash:

рН pH was defined as pH = - log10[H+], where [H+] is the molarity (moles per liter) of H+ in a solution containing a solvent and one or more solutes. The pH scalevaries from less than 0 (lots of H+ and very acidic) to greater than 14 (very little H+ and very basic or alkaline). Neutral pH, the pH of distilled water, is 7.0. At this pH, the molarity of H+ is10-7 mol L-1.

Carbonic Acid Water can be acidified in one of several ways. When gas-phase carbon dioxide dissolves in water, it reacts rapidly with a water molecule to form aqueous carbonic acid [H2CO3(aq)], a weak acid, which dissociates by the reversible reactions

A fraction of CO2(g) always dissolves in rainwater. Thus, rainwater, even in the cleanest environment on Earth, is naturally acidic due to the presence of background carbonic acid in it. The pH of rainwater affected by only carbonic acid is about 5.6, indicating that its hydrogen ion olarity is 25 times that of distilled water.

Sulfuric Acid When gas-phase sulfuric acid condenses onto rain drops, the resulting aqueous-phase sulfuric acid [H2SO4(aq)], a strong acid, dissociates by

Nitric acid When gas-phase nitric acid dissolves in raindrops, it forms aqueous nitric acid [HNO3(aq)], a strong acid that dissociates almost completely by

Hydrochloric Acid When gas-phase hydrochloric acid dissolves in raindrops, it forms aqueous hydrochloric acid [HCl(aq)], a strong acid that dissociates almost completely by

Sources of Acids Some of the enhanced acidity of rainwater from sulfuric acid, nitric acid, and hydrochloric acid is natural. Volcanos, for example, emit SO2(g), a source of sulfuric acid, and HCl(g). Phytoplankton over the oceans emit dimethylsulfide [DMS(g)], which oxidizes to SO2(g). The main natural source of HNO3(g) is gas-phase oxidationof natural nitrogen dioxide [NO2(g)]. The addition of natural acids to rainwater containing carbonic acid results in typical natural rainwater pHs of between 5.0 and 5.6

Sources of Acids Acid deposition occurs when anthropogenically produced acids are deposited to the ground, plants, or lakes in dry or wet form. The two most important anthropogenically produced acids today are sulfuric and nitric acid, although hydrochloric acid can be important in some areas. In the eastern United States, about 60 to 70 percent of excess acidity of rainwater is due to sulfuric acid, whereas 30 to 40 percent is due to nitric acid. Thus, sulfuric acid is the predominant acid of concern. In polluted cites where fog is present, such as in Los Angeles, California, nitric acid fog is a problem. In locations where HCl(g) is emitted anthropogenically, such as near wood burning or industrial processing, HCl(aq) affects the acidity of rainwater. Today, however, HCl(aq) contributes to less than 5 percent of total rainwater acidity by mass. Other acids that are occasionally important in rainwater include formic acid [HCOOH(aq), produced from formaldehyde] and acetic acid [CH3COOH(aq), produced from acetaldehyde and the main ingrediant in vinegar].

Sulfuric Acid Deposition The most abundant acid in the air is usually sulfuric acid [H2SO4(aq)], whose source is sulfur dioxide gas [SO2(g)], emitted anthropogenically from coal-fire power plants, metalsmelter operations, and other sources.

Power plants usually emit SO2(g) from high stacks so that the pollutant is not easily downwashed to the surface nearby. The higher the stack, the further the wind carries the gas before it is removed from the air. The wind transports SO2(g) over long distances, sometimes hundreds to thousands of kilometers. Thus, acid deposition is often a regional and long-range transport problem. When acids or acid precursors are transported across political boundaries, they create transboundary air pollution.

the S(IV) and S(VI) families

Gas-Phase Oxidation of S(IV)

Aqueous-Phase Oxidation of S(IV)

Nitric acid deposition

Effect of acid deposition. London-type smog were recorded in London in the IX and XX centuries. December 1873 (270–700 deaths more than the average rate), January 1880 (700–1,100 excess deaths), December 1892 (1,000 excess deaths), November 1948 (300 excess deaths), December 1952 (4,000 excess deaths), January 1956 (480 excess deaths), December 1957 (300–800 excess deaths), December 1962 (340–700 excess deaths). Excess deaths occurred in every age group, but the number was greater for people older than 45. People with a history of heart or respiratory problems made up 80 % of those who died. During the episodes, temperature inversions coupled with fog and heavy emissions of pollutants, particularly from combustion of coal and other raw materials, were blamed for the disasters. During the 1952 episode, peak concentrations of SO2(g) and particulate smoke were estimated to be 1.4 ppmv and 4,460 g m3, respectively. The particle and fog cover was so heavy during that event that the streets of London were dark at noontime, and it was necessary for buses to be guided by lantern light.

Effect of acid deposition. Effects on Lakes and Streams Effects on Biomass

Effect of acid deposition Effects on Buildings and Sculptures

Acidification in the Arctic

Sources Industrial areas farther south contribute to Arctic air pollution Most sulfur in Arctic air comes from industrial areas further south. Eurasia (40 percent) and eastern North America (20 percent) are the major global sources. A large part of the remaining global emissions occur in the Far East, particularly China. Emissions of sulfur dioxide have decreased considerably in North America and Europe after a peak in the late 1970s and early 1980s. This results from an interplay of political decisions to cut emissions, the replacement of ‘dirty’ fuels, and new technologies for removing sulfur from fossil fuel and for cleaning flue gases in power plants. Nonetheless, power generation and smelting remain major sources.

Sources outside the Arctic

Natural sources The algae in ocean surface waters are a source of sulfur to the atmosphere in the form of dimethylsulfide (DMS: СН3 – S - CH3), which is oxidized in the atmosphere to sulfur dioxide, sulfate and methyl sulfonic acid (MSA: CH3SO3H). Emissions of reduced sulfur compounds from terrestrial environments and vegetation are about one order of magnitude smaller than the marine emissions. Volcanic emissions of sulfur include both hydrogen sulfide (H2S), elemental sulfur and sulfur dioxide. The emissions are located in areas of volcanic activity and are extremely variable from one year to another. Annual emissions of sulfur from volcanoes between 1964 and 1972 have been estimated at 7.8 Tg S/y.

Ammonia (NH3) is also involved in acidification processes; it is a neutralizing compound in the atmosphere, but acts as a net acidifying agent in soils. Ammonia combines with sulfuric acid in the atmosphere to form (NH4)2SO4, NH4HSO4 and other semi neutralized sulfates. Acidification is not solely a function of sulfate (or nitrate) deposition but is also controlled by the base cations (Ca2+,Mg2+, K+, Na+) contained in aerosols or precipitation. There is considerable evidence that recent declines in sulfate levels have occurred together with an accompanying decrease in base cations. While some of these base cations can be argued to have a natural source (e.g., soil dust), European decreases in base cations have been attributed to an anthropogenic decrease. For the latter reason, decreases in emissions of sulfur species may not result in an equivalent decrease in acidity.

Sources within the Arctic Metal smelters have the largest emissions within the Arctic Production of copper, nickel and other nonferrous metals from sulfur-bearing ores create the largest emissions of acidifying substances within the Arctic. The traditional smelting method roasts the ore to remove the sulfur as sulfur dioxide and to oxidize the iron in the ore before further smelting and refining. The sulfur dioxide can be recovered in modern smelters and used as a raw material for producing sulfuric acid, gypsum, and some other inorganic chemicals. Most smelter emissions come from the Nikel, Zapolyarnyy, and Monchegorsk complexes on the Kola Peninsula and from Norilsk in northwestern Siberia. Compared with similar industries in other areas, emissions from these smelters are extremely high. Norilsk is the largest source, spewing out more than a million tonnes of sulfur every year.

Sources within the Arctic Exploitation and usage of fossil fuels Within the Arctic, there is coal mining on Spitsbergen (Norway), in Vorkuta (Russia) and in the Tiksi region (northeastern Siberia). Moreover, there is a large coal mining area in the Pechora Basin, which lies just south of the Arctic Circle in northern Russia. Because of the small number of inhabitants in much of the Arctic, fuel and energy consumption is low and the emissions from the usage of fossil fuels are mainly located in towns. For example, there are coal-fired power plants in Vorkuta and Inta (Russia), which serve the local settlements, and coal mining and oil and gas exploration in these areas. Other examples include the mining settlements on Spitsbergen which are also served by small, coal-fired electric power plants in Longyearbyen and Pyramiden.

Sources within the Arctic Shipping and fishing activities are also sources of air pollutants in the Arctic. For example, extensive deep-sea fishing for cod, capelin and prawns takes place in the Barents Sea. Marine transport, particularly of timber and timber products, is also important along the Siberian coast and on the Siberian rivers.

Natural emissions There are areas of volcanic activity in the North Atlantic and Bering Sea regions, and in southern Alaska, however, the associated sulfur emissions are relatively low and sporadic. A notable area with respect to natural emissions of sulfur is the Smoking Hills area in Canada, where the ‘natural’ combustion of pyrite-bearing bituminous shale, releasing sulfur dioxide and sulfuric acid mist and aerosol, has caused phytological damage within 500 m of the source. However, these emissions are relatively low compared to anthropogenic inputs. The Arctic Ocean and adjacent seas are generally quite productive and hence the biogenic production of dimethylsulfide (DMS) and transport of DMS through the sea-air interface must be considered a potential source of atmospheric sulfur.

Natural emissions In winter, anthropogenic sources account for almost all of the sulfur in the Arctic atmosphere, whereas in summer about 30% of the sulfur is from natural sources.

Local energy production is a small source Emissions from energy production in the Arctic are generally low because the population is sparse. There are coal-fired power plants in Vorkuta and Inta in Russia, serving local settlements around coal mines and gas fields in the area. The mining settlements on Spitsbergen also have coal-fired power plants. Shipping and fishing fleets are also sources of sulfur. The extensive fishing fleet in the Barents Sea uses large amounts of diesel fuel. Marine transport, particularly of timber and timber products, is important along the Siberian coast and on Siberian rivers.

Nitrogen emissions are less important Burning of fossils fuels also creates nitrogen oxides. In more densely populated areas, traffic and power production are the most important sources. Emissions increased rapidly from the 1950s to 1975. In North America and Europe, they have remained fairly constant since 1980. Nitrogen oxides contribute to acidification in non-Arctic parts of Europe and North America, but are less important in the Arctic context.

Atmospheric processes The fate of sulfur and nitrogen emissions depends on what happens in the atmosphere. Light, moisture, and reactive chemical compounds in the air act together to transform sulfur dioxide and nitrogen oxides into acid precipitation and into particles that can settle on surfaces they encounter. The box to the left describes the air chemistry of sulfur. When air from mid-latitudes moves northward with its load of contaminants, it rises, forming layers of dirty air at higher altitudes. However, pollution released into the Arctic airmass tends to remain within a couple of kilometers of the ground because of temperature inversions that create a lid of cold air. In the spring and winter, lack of precipitation in the High Arctic keeps acidifying contaminants suspended in the air. Sparse vegetation also provides for low deposition rates of particulate matter. During summer, two mechanisms keep the air cleaner: first, the northward shift of the Arctic front, away from major source regions, reduces contaminant inputs, and second, increased precipitation washes acid contaminants out of the air.

The atmospheric chemistry of the sulfur cycle The atmospheric chemistry of the sulfur cycle is dominated by OH radical reactions in the gas phase with H2S, DMS, and SO2, all of which lead to the production of gaseous sulfuric acid (H2SO4), and by gaseous and aqueous phase reactions between SO2 and hydrogen peroxide (H2O2) and ozone (O3). Once sulfate is produced, its removal is relatively rapid with an atmospheric half-life in the order of 3 to 7 days at mid-latitudes and about two weeks or more in the High Arctic during winter. The atmospheric emission, production, transport and deposition cycle of sulfate aerosol (whether sulfuric acid or ammoniated sulfate compounds such as (NH4)2SO4 and NH4HSO4) has been the subject of intense research activity during the last 20 years There are transport and chemical processes in the sulfur cycle that are strongly latitude-dependent. The lack of sunlight in the Arctic for large parts of the year limits the production of the OH radical and H2O2. The former is produced from the photodissociation of ozone in clean air and, incrementally, from hydrocarbon radicals in more polluted areas. Lower OH and H2O2 concentrations in winter slow the sulfate production cycle and increase the SO2/SO42–ratio observed in the Arctic. This photochemical mechanism is critical to the timing of the Arctic haze maximum The seasonality of SO2 oxidation to sulfate is important in prolonging the presence of sulfate aerosols in the Arctic into April and May.

Nitrogen chemistry Nitric oxide (NO) and nitrogen dioxide (N02) are the two most important nitrogen oxide air pollutants. They are frequently lumped together under the designation NOx , although analytical techniques can distinguish clearly between them. Of the two, N02 is the more toxic and irritating compound. Nitric oxide is a principal by-product of combustion processes, arising from the high-temperature reaction between N2 and O2 in the combustion air and from the oxidation of organically bound nitrogen in certain fuels such as coal and oil. The oxidation of N2 by the O2 in combustion air occurs primarily through the two reactions

Effect in the Arctic Loss of soil fertility contributes to tree death Most Arctic mineral soils are naturally acidic, because slow weathering limits the rate at which they can replace the base ions that trees use for nutrients. Acid deposition amplifies this natural acidification process when hydrogen ions replace base ions, causing the base ions to leach further down into the soil or to be washed away in runoff. Tree damage from acidification has many causes, but the lack of nutrients and the excess of aluminum ions are two important culprits. The figure shows the pH at which different base ions become mobile.

Effect in the Arctic Sulfur dioxide has damaged the forest, killed lichens and some shrubs Sensitive invertebrates have disappeared