Organic acids in rain

As a prerequisite for GC, organic acids have to be concentrated and derivatized. Extraction is usually accomplished by liquid/liquid extraction or SPE. In all drinking water methods listed in Table 13.3, the extraction step was preceded by aqueous derivatization of a ketofunction, thus limiting these GC methods to ketoacids. " Simple, aliphatic mono- and dicarboxylic acids cannot be determined with these methods. However, approaches taken for GC analysis of organic acids in rain could be equally as well applied to drinking water, thus covering additional mono- and dicarboxylic acid. " " - °... 

Kawamura, K. and Kaplan, I. R., Capillary G.C. determination of volatile organic acids in rain and fog samples, Anal. Chem., 56, 1616-1620, 1984. 

Why Do We Need to Know This Material Chapter 9 developed the concepts of chemical equilibria in gaseous systems this chapter extends those ideas to aqueous systems, which are important throughout chemistry and biology. Equilibria between acids, bases, and water in plant and animal cells are vital for the survival of individual organisms. To sustain human societies and protect our ecosystems, we also need these ideas to understand the acidity of rain, natural waters such as lakes and rivers, and municipal water supplies. 

Hydrogen chloride and chlorine gases form when chlorinated organic compounds in hazardous wastes are burned. If uncontrolled, this chlorine can become a human health risk and is a large component in the formation of acid rain. U.S. EPA has developed different requirements to control the emissions of chlorine from the different classes of combustion units. 

Acid rain harms the environment in a number of ways it dissolves many rocks and metals, alters the composition of soils, groundwaters, and lakes, and alters the environmental conditions of living organisms. Acid rain is also particularly harmful to ancient objects and structures, as it plays an important role in their deterioration and sometimes total destruction. Unprotected limestone, marble, and sandstone, all of them widely used in ancient times for building and making statuary, are disintegrated by acid rain, which... 

As a result of microbial formation of metal-organic complexes with fulvic acids in soils of Tropical Rain Forest ecosystems, the surface and sub-surface runoff waters are enriched in some heavy metals like manganese and copper. A similar tendency has been shown for boron, strontium and fluorine. 

As regards the pollutants monitoring, from the measurements available so far it could be concluded that acid rain is coming to be a major problem in Asia. In many industrially developed and new developed countries such as Japan, China, Taiwan, South Korea, Thailand etc., values of pH <5 are encountered at many sites, and they represent more than 50% of monitored rain events on a regional scale. In some developing countries of South-East Asia (Myanmar, Laos, Cambodia) most rainwater pH measurements tend to be around 5.6, the pH of natural rainwater, and the acid rain precipitation is mainly due to localized industrial pollution. There is some evidence that pH values below 5 at unpolluted sites may be due to the contribution of weak organic acids, such as formic and acetic acids (Radojevic, 1998). 

Liming an acidic lake is similar to the process many people use to maintain a pH balance in their soil for lawn maintenance. Plants have an optimum pH range in which they strive. Acidic conditions often develop in soils for several reasons. Rain tends to leach away basic ions, weak organic acids develop from the carbon dioxide produced by decaying organic matter, and strong acids, such as nitric acid, can form when ammonium fertilizers oxidize. To neutralize these acids, different forms of lime such as quicklime, CaO, and slaked lime, Ca(OH)2, are used to neutralize the acid and increase the pH of the soil. Table 13.9 shows how much fertilizer is wasted when applied to... 

In areas where the geology is dominated by granite, lakes have less buffering capacity and are much more susceptible to the impacts of acid rain. Fish and aquatic organisms differ in their ability to adapt to acidic conditions. The natural pH of lakes is approximately 8.0. The pH of poorly buffered lakes is between 6.5 and 7.0. The effects of pH on different aquatic organisms are summarized in Table 18.1. 

Acid rain arises from the oxidation of S02 and N02 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 fOOO km or more. Thus both short-range and long-range transport must be considered. 

While nitric acid is one of the major contributors to acid deposition (more colloquially acid rain ), we treat its chemistry separately from that of sulfuric and organic acids discussed in the following chapter. The reason for treating it first is that the chemistry of... 

Organic acids can be removed by reaction with OH (see Chapter 6.H) as well as by wet or dry deposition. As a result, these acids are a common component of rain, clouds, fogs, and dews as would be expected from their large Henry s law constants, 103-104 mol L l atm-1 (see Keene et al., 1995), and are found in the condensed phase from remote to highly polluted urban areas (e.g., see Norton, 1985 Keene and Galloway, 1986, 1988 Likens et al., 1987 Weathers et al., 1988 Muir, 1991 Sakugawa et al., 1993 Keene et al., 1995 and Khwaja et al., 1995). 

Acids and bases are two of the most common types of substances in the laboratory and the everyday world. We need to know how to recognize them, what their characteristic reactions are, and why they are such important chemicals. We shall see that keeping the concentrations of acids and bases in plant and animal cells within certain limits is necessary for the survival of individual organisms, and controlling the acidity of rain, of natural waters such as lakes and rivers, and of municipal water supplies is necessary to sustain human societies. 

DMS is photochemically oxidized in the atmosphere to methanesulfonic and sulfuric acids. These strong acids contribute, along with nitric and organic acids, to the natural acidity of precipitation. Recent problems with acid rain have aroused interest in the anthropogenic and natural sources of volatile sulfur compounds (2). 

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