Acid deposition reduction

Since SO2 and NO2 are criteria pollutants, their emissions are regulated. In addition, for the purposes of abating acid deposition in the United States, the 1990 Clean Air Act Amendments require that nationwide SO2 and NO emissions be reduced by approximately 10 million and 2 million t/yr, respectively, by the year 2000. Reasons for these reductions are based on concerns which include acidification of lakes and streams, acidification of poorly buffered soils, and acid damage to materials. An additional major concern is that acid deposition is contributing to the die-back of forests at high elevations in the eastern United States and in Europe. 

A variety of models have been developed to study acid deposition. Sulfuric acid is formed relatively slowly in the atmosphere, so its concentrations are beUeved to be more uniform than o2one, especially in and around cities. Also, the impacts are viewed as more regional in nature. This allows an even coarser hori2ontal resolution, on the order of 80 to 100 km, to be used in acid deposition models. Atmospheric models of acid deposition have been used to determine where reductions in sulfur dioxide emissions would be most effective. Many of the ecosystems that are most sensitive to damage from acid deposition are located in the northeastern United States and southeastern Canada. Early acid deposition models helped to estabUsh that sulfuric acid and its precursors are transported over long distances, eg, from the Ohio River Valley to New England (86—88). Models have also been used to show that sulfuric acid deposition is nearly linear in response to changing levels of emissions of sulfur dioxide (89). 

A second area of concern is reduced tree growth in forests. As acidic deposition moves through forest soil, the leaching process removes nutrients. If the soil base is thin or contains barely adequate amounts of nutrients to support a particular mix of species, the continued loss of a portion of the soil minerals may cause a reduction in future tree growth rates or a change in the types of trees able to survive in a given location. 

Table 12-4 are sufficient for an understanding of smog chemistry. The major undesirable components of photochemical smog are NOj, O3, SOj, H2SO4, PAN, and aldehydes. Air quality standards have been established in several countries for SO2, NO2, and O3 H2SO4 contributes to acidic deposition and reduction in visibility and PAN and aldehydes can cause eye irritation and plant damage if their concentrations are sufficiently high. 

Acid deposition is a regional problem wherever large amounts of fossil fuels are consumed. There have been significant efforts in both Europe and North America to reduce acid deposition because of its many deleterious effects. This effort has focused mainly on the reduction of SO, emissions. In the future acid deposition tvill have to be addressed in eastern Asia, where rapid industrialization and increased use of fossil fuels is likely. 

Bio-ethanol is attracting growing interests in relation to the shift of raw materials from petroleum to biomass. A pioneering work by Christensen is that over MgAl203 support gold is much more selective to acetic acid than palladium and platinum in the aerobic oxidation of ethanol in water in a batch reactor. Figure 32 shows that selectivity to acetic acid exceeds 80% [99]. In contrast, Au/Si02 catalysts prepared by deposition reduction... 

The critical load concept is intended to achieve the maximum economic benefit from the reduction of pollutant emissions since it takes into account the estimates of differing sensitivity of various ecosystems to acid deposition. Thus, this concept is considered to be an alternative to the more expensive BAT (Best Available Technologies) concept (Posch et al., 1996). Critical load calculations and mapping allow the creation of ecological-economic optimization models with a corresponding assessment of minimum financial investments for achieving maximum environmental protection. 

Since environmental damage due to acid deposition has largely been limited to the eastern parts of Canada (east of the Manitoba-Ontario border) and the USA (east of the Mississippi River), most of the emission reductions have occurred in those areas. Figure 8 illustrates the SO2 emission totals in eastern Canada, eastern USA and total North America. 

The inventory made by Buijsman in the Netherlands should be caracterised as a quite rough estimate. This is demonstrated by the assumptions on which he based his calculations. For instance he neglected the emission from stables for laek of reliable data. If the Government wants to reduce the acid precipitation, there will be paid attention to ammonia. As it is released from ground level sources reduction of ammonia emission has more effect on acid deposition in the region than in the case with S02 and NOx. 

Acid deposition can cause acidification of soils and waters. Acidification can be defined as a reduction of the acid-neutralizing capacity of soils or waters. The acidneutralizing capacity is also known as alkalinity (AUc) and indicates the sensitivity of a water system toward acidification. It can be expressed as [9] ... 

Efforts to reduce acid deposition have had mixed results thus far. For example, measurements at five locations in Nova Scotia, New Brunswick, Newfoundland, and Labrador by Canadian researchers found that sulfate deposition dropped between 27 and 50 percent between 1980 and 1995. During the same time, however, there was a significant reduction in acid deposition at only one of the five monitoring sites. 

Attention has been focused recently on sedimentary microbial reduction of sulfate. This process neutralizes atmospheric sulfuric acid deposited into soft-water lakes (8-10) through the production of two equivalents of alkalinity per mole of sulfate reduced (11). 

Acid rain control will produce significant benefits in terms of lowered surface water acidity. If acidic deposition levels were to remain constant over the next 50 years (tlie time frame used for projection models), the acidification rate of lakes in the Adirondacks that are larger than 10 acres would rise by 50 percent or more. Scientists predict, however, that the decrease in SO emissions required by the Acid Rain Program will significantly reduce acidification due to atmospheric sulfui Without the reductions in SO2 emissions, the proportions of aquatic systems in sensitive ecosystems that are acidic would remain high or dramatically worsen. 

A second area of concern is that of reduced tree growth in forests. The leaching of nutrients from the soil by acid deposition may cause a reduction in future growth rates or changes in the type of trees to those able to survive in the altered environment. In addition to the change in soil composition, there are the direct effects on the trees from sulfur and nitrogen oxides as well as ozone. 

Ultimately the mitigation to the environmental effects of acid deposition requires decrease in exposure through emission reduction. There has been considerable debate about how much and where reductions can be achieved from practical planning for SO and NO ... 

Uranium deposited by wet or dry precipitation will be deposited on land or in surface waters. If land deposition occurs, the uranium can be reincorporated into soil, resuspended in the atmosphere (typically factors are around 10 ), washed from the land into surface water, incorporated into groundwater, or deposited on or adsorbed onto plant roots Gittle or none enters the plant through leaves or roots). Conditions that increase the rate of formation of soluble complexes and decrease the rate of sorption of labile uranium in soil and sediment enhance the mobility of uranium. Significant reactions of uranium in soil are formation of complexes with anions and hgands (e.g., COj, OH ) or humic acid, and reduction of U" " to U. Other factors that control the mobility of uranium in soil are the oxidation-reduction potential, the pH, and the sorbing characteristics of the sediments and soils (Allard et al. 1979, 1982 Brunskill and Wilkinson 1987 Herczeg et al. 1988 Premuzie et al. 1995). 

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