Acid precipitation, role

Acidity, definition in relation to possible ecosystem responses, 38,41 Acid precipitation, role of HO, 75 Acid rain... 

Other workers (115-124 for example) have also centered their efforts on the role of phytic acid on zinc and iron bioavailabiliy from both soy and wheat products. It has been suggested (120) that the phytate-to-zinc molar ratio could be used to predict zinc bioavailability in high-phytate foods. Several groups (115, 117), including ours (113), 1 least partially supporT this hypothesis. However, recent work from our laboratory (112) involving soy protein of similar phytate-to-zinc molar ratios clearly demonstrates that zinc bioavailability is also altered by food processing. In this study, zinc from neutralized soy concentrates and isolates was shown to be less available to the rat than was the corresponding acid-precipitated products. This is unfortunate as alkaline conditions are commonly utilized for soy and other plant proteins to obtain beneficial functional properties. 

Globally, the oxides of nitrogen, NO (nitric oxide), NO2 (nitrogen oxide), and N2O (nitrous oxide), are key species involved in the chemistry of the troposphere and stratosphere. NO and N2O are produced mostly by microbial soil activity, whereas biomass burning is also an important source of NO. Nitric oxide is a species involved in the photochemical production of ozone in the troposphere, is involved in the chemical produaion of nitric acid, and is an important component of acid precipitation. Nitrous oxide plays a key role in stratospheric ozone depletion and is an important greenhouse gas, with a global warming potential more than 200 times that of CO2. 

There is considerable interest in volcanic emissions of sulfur compounds because of the role of atmospheric sulfur chemistry in atmospheric radiation and climate, the hydrological cycle, acid precipitation, and air quality (see Chapter 8.14). Early theories on the climatic effects of eruptions considered that ash particles were responsible for raising the planetary albedo, but it is now clear that even fine tephra sediment rapidly from the atmosphere, and that the main protagonist in volcanic forcing of climate is the... 

Wiklander L. (1975) The role of neutral salts in the ion exchange between acid precipitation and soil. Geoderma 14, 93-105. 

The conditions and procedures of precipitation play a significant role in catalyst morphology, texture, pore structure, physical strength, and consequently the performance (activity, selectivity, and stability) of the catalyst. By merely changing the sequence of solution addition, catalyst components can be precipitated simultaneously or sequentially. The methods of precipitation most often used are constant pH coprecipitation, sequential precipitation, acid-to-base precipitation, and base-to-acid precipitation. 

To put these in perspective, it should be pointed out that soils in humid regions naturally acidify, even without the addition of any man-made pollution. The role of additional acidic precipitation is simply to increase the rate of acidification. Our activities, such as the addition of nitrogen fertilizers, accelerate acidification of the soil much more rapidly than any recorded acid precipitation. 

Very little has been documented concerning the role of ammonium except that it is a recognised component of acid precipitation. There is a correlation between the ions 804 "/ 3 and NH4 in acid precipitation, but the proportions of each will vary according to sulphur and nitrogen budgets and the rate of ammonia released to the atmosphere from biological processes and from fertilizers. 

The role of acid precipitation in causing soil acidification is examined below. 

Nitrogen oxides play an important role in the photochemistry of the troposphere, controlling the formation of tropospheric O3, affecting the concentration of the hydroxyl radical, and contributing to acid precipitation. Nitrogen dioxide (NO2) is one of the most important reactive nitrogen species its photolysis is the primary source of O3 in the troposphere (see Section 28.6 for further details on the actual chemical processes and rates). 

Regarding the accelerated leaching potential of acidic precipitation, several aspects have to be considered, if the effective leaching flux is to be assessed they may be categorized as follows i) physico-chemical properties of the precipitation, ii) physico-chemical conditions of the interface precipitation-leaf surface, iii) biological characteristics of the leaves and in particular of their surfaces. Some of these aspects will be addressed up on later to point out their crucial role in determining the quantity and quality of the leachates. 

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