CO2aq CO2g H2Ol 2HCO3aqeqn

This reaction makes seawater about eight times more effective at absorbing CO2 than a solution of similar ionic strength but not containing CO2-. The discussion above assumes that equilibrium is achieved between the sea-water and the air with respect to CO2. This leads to the second factor which must be taken into account, since the slow mixing time of the oceans means that it takes hundreds, if not thousands, of years for equilibrium to be attained over the whole depth. In general, it is not...

Composition of the atmosphere

Bulk composition of the atmosphere is quite similar all over the Earth because of the high degree of mixing within the atmosphere. This mixing is driven in a horizontal sense by the rotation of the Earth. Vertical mixing is largely the product of heating of the surface of the Earth by incoming solar radiation. The oceans have a much slower mixing rate, but even this is sufficient to ensure a relatively constant bulk composition in much the same way as the atmosphere. However, some parts of the...

Contaminated land

In exceptional cases, the rocks, minerals and soils of the land surface contain compounds that generate natural chemical hazards. Uranium (U) and potassium (K), common elements in granitic rocks, are inherently unstable because of their radioactivity (see Section 2.8) and radioactive decay of isotopes of uranium to form radon (Rn) gas can be a health hazard (Box 4.13). Some chemicals, such as herbicides and pesticides, are present in soils because we put them there intentionally. Other...

Coordination of ions and the radius ratio rule

In crystals where bonding is largely ionic (see Section 2.3.2), the densest possible packing of equal-sized anions (represented by spheres) is achieved by stacks of regular planar layers, as shown in Fig. 4.3. Spheres in a single layer have hexagonal symmetry, i.e. they are in symmetrical contact with six spheres. The layers are stacked such that each sphere fits into the depression between three other spheres in the layer below. Fig. 4.2 Structure of SiO4 tetrahedron. (a) Silicon and oxygen...

Element chemistry

The 20 largest rivers on Earth carry about 40 of the total continental runoff, with the Amazon alone accounting for about 15 of the total. These rivers give the best indication of global average riverwater chemical composition, which can be compared with average continental crust composition (Table 5.1). Three features stand out from this comparison 1 Four metals dominate the dissolved chemistry of freshwater, all present as simple cations (Ca2+, Na+, K+ and Mg2+). 2 The low concentration of...

Estuarine processes

There are many differences between the chemistry of continental surface waters and seawater. In particular, seawater has a much higher ionic strength than most continental water (see Fig. 5.3) and seawater has a huge concentration of sodium and chloride ions (Na+ and Cl-) (Table 6.1), in contrast with calcium bicarbonate-dominated continental waters (see Section 5.3). Seawater is a high-concentration chemical solution, such that mixing only 1 (volume) of seawater with average riverwater...

FeS2s14Feq8H20 a 15Feq 2S04aq 16Haq

At pH values much above 3 the iron(III) precipitates as the common iron(III) oxide, goethite (FeOOH) Fe(+q)+ 2H2O(l) FeOOH(s) + 3H+aq) eqn. 5.18 The precipitated goethite coats stream beds and brickwork as a distinctive yellow-orange crust (Plate 5.2, facing p. 138), a very visible manifestation of the problem. Bacteria use iron compounds to obtain energy for their metabolic needs (e.g. oxidation of ferrous to ferric iron). Since these bacteria derive energy from the oxidation of inorganic...

Formation of soils

So far we have discussed the mechanisms and solid products of chemical weathering without precise consideration of the environment in which these reactions occur. While chemical attack of exposed bedrock surfaces can happen, most weathering reactions occur in (or under) soils. We have already noted that the oxidation of soil organic matter causes acidity of natural waters (Section 4.4.2), promoting chemical weathering. This acknowledges the important role of soils in environmental chemistry. So...

Further reading

Cox, R.A., Hewitt, C.N., Liss, P.S., Lovelock, J.E., Shine, K.R. & Thrush, B.A. (eds) (1997) Atmospheric chemistry of sulphur in relation to aerosols, clouds and climate. Philosophical Transactions of the Royal Society of London 352B, 139-254. IPCC (2001) Climate Change 2001 The Scientific Basis. Contribution of Working Group I to the Third Assessment Report, Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge. Jones, K.C and De Voogt, P. (1999) Persistent...

Global persistent organic polllutant equilibrium

The manufacture and use of many exotic organic compounds (see Section 1.4) has now been discontinued because of their persistence, potential health effects and global mobility. For example, PCBs were first manufactured and used in the 1930s and their usage increased until the early 1970s. Thereafter PCB usage was banned in many instances or subject to restrictions. However, PCBs did not immediately disappear from the environment. Even today PCBs are present in all of Earth's environmental...

HgO Hg2 H2Oeqn 523

This ionic mercury (HgII) adheres to aerosols and thus has a short (days to weeks) residence time in the atmosphere rainfall delivers it to the local soils and rivers. Ionic mercury is readily methylated (eqn. 5.24) by both abiotic and biotic pathways. However, most scientists now agree that methylation by anaerobic sulphate reducing bacteria (SRB) is most important. In equation 5.24 the Hg2+ ion forms a covalent compound dimethylmercury (Hg(CH3)2) by bonding with the methyl anion (CH-). The...

H2SO4aq CaCO3S H2Ol CO2g CaSO4S2H2Ow eqn 328

Sulphuric acid converts limestone (CaCO3) into gypsum (CaSO4 .2H2O). The deterioration is severe because gypsum is soluble and dissolves in rain. Perhaps more importantly, gypsum occupies a larger volume than limestone, which adds mechanical stress so that the stone almost explodes from within. The diesel engine is no longer confined to large vehicles in Europe, as passenger cars have taken advantage of potentially lower fuel costs. The fuel injection process of the diesel engine leads to the...

Human effects on biogeochemical cycles

In discussing the chemistry of near-surface environments on Earth it is important to distinguish between different types of alteration to Earth systems caused by humans. Two main categories can be distinguished 1 Addition to the environment of exotic chemicals as a result of new substances synthesized and manufactured by industry. 2 Change to natural cycles by the addition or subtraction of existing chemicals by normal cyclical and or human-induced effects. The first category of chemical change...

Human effects on regional seas 2 the Gulf of Mexico

The Mississippi river system is one of the largest in the world and drains over 40 of the USA, discharging into the Gulf of Mexico through a large and complex delta near New Orleans (Fig. 6.31). The river system drains intensively farmed areas of the USA and nitrate (NO-) concentrations in the river doubled from the 1960s to the 1980s as a result of increased fertilizer use (Fig. 6.31). Since the 1980s NO- concentrations have remained at this high level (see also Section 5.5.1). Increased...

Info

Fig. 4.33 Aerobic biodegradation pathways for benzene. Fig. 4.34 Biodegradation pathways for naphthalene. dihydroxynaphthalene (Fig. 4.35). Degradation then proceeds as shown for naphthalene (Fig. 4.34). At the Burlington Northern site the creosote-contaminated soil was sieved and then ball milled to reduce particle size, a process that increases contaminant availability by increasing reactive surface area. The milled creosote-contaminated soil was then slurried with water and placed in five...

Internet search keywords

Marine biogeochemistry seawater chemistry estuarine chemistry ionic strength halmyrolysis microbial activity estuaries phytoplankton estuaries oxygen estuaries sewage estuaries major ions seawater sea air fluxes evaporites calcium carbonate seawater pyrite marine sediment hydrothermal processes black smokers element distribution oceans minor components seawater conservative ions seawater nutrients seawater scavenging seawater phosphate seawater nitrate seawater iron seawater ocean circulation...

Ion exchange and soil pH

Exchangeable ions are those that are held temporarily on materials by weak, electrostatic forces. If particles with one type of adsorbed ion are added to an electrolyte solution containing different ions, some of the particle-surface adsorbed ions are released into solution and replaced by those from the solution (Fig. 4.20). We have seen that the interlayer sites of clay minerals, particularly smectites, hold ions weakly, giving these minerals a capacity for ion exchange. Clay mineral ion...

Minor chemical components in seawater

Gases dissolve from the atmosphere into the oceans according to the Henry's law constant (see Box 3.4). In the absence of biological processes the ocean surface waters would therefore be saturated with all atmospheric gases. Some of these gases, such as argon (Ar) and helium (He), are chemically inert, while others such as nitrogen gas (N2) are available as a nutrient source to only a few specialized nitrogen-fixing organisms and are hence effectively inert in seawater, and thus very close to...

Naaq Claq NaClSeqn

And, in addition, some magnesium (Mg) salts begin to crystallize if evaporation continues, highly soluble potassium (K) salts precipitate (Box 6.2). The problem with invoking evaporation as a removal mechanism for ions in seawater is that there are currently very few environments in which evaporite salts are accumulating to a significant extent. This is because enormous volumes of seawater need to be evaporated before the salts become concentrated enough to precipitate. Clearly this cannot...

Natural sources

Since the atmosphere can be treated, on a large scale, as if it were in steady state, we have a model that views the atmosphere as having sources, a reservoir (i.e. the atmosphere itself) and removal processes, all in delicate balance. The sources need to be quite stable over the long term. If they are not, then the balance will shift. In terms of our earlier analogy, the level in the leaking bucket will change. The best-known, and most worrying, example of such a shift is the increasing...

Ocean circulation and its effects on trace element distribution

The preceding discussion of trace elements in seawater has assumed that the oceans have a uniform, warm, nutrient-depleted surface mixed layer and a static deep zone. In fact, at high latitudes surface seawater is cold enough to destroy any density stratification, mixing the oceans to depths of up to 1000 m. This dense surface water sinks and flows slowly into the centre of the oceans as a layer of Fig. 6.26 Chlorophyll concentrations as indicators of phytoplankton growth, inside and outside an...

Order in the elements

Most of the chemistry in this book revolves around elements and isotopes (see Box 1.1). It is therefore helpful to understand how the atomic number (Z) of an element, and its electron energy levels allow an element to be classified. The electron is the component of the atom used in bonding (Section 2.3). During bonding, electrons are either donated from one atom to another, or shared in either case the electron is prised away from the atom. One way of ordering the elements is therefore to...

Organic moleculesstructure and chemistry

Organic matter and organic compounds are integral components of all environmental reservoirs it is therefore important to understand some of the basic facts about their structure and chemistry. Organic molecules contain carbon, hydrogen and often some other non-metallic elements such as oxygen, nitrogen, sulphur or halogens such as chlorine. Organic molecules are often complex structures, typically a skeleton of carbon atoms arranged in chains, branched chains or rings. It is more convenient to...

Origin and evolution of the Earth

The planets of our solar system probably formed from a disc-shaped cloud of hot gases, the remnants of a stellar supernova. Condensing vapours formed solids that coalesced into small bodies (planetesimals), and accretion of these built the dense inner planets (Mercury to Mars). The larger outer planets, being more distant from the sun, are composed of lower-density gases, which condensed at much cooler temperatures. As the early Earth accreted to something like its present mass some 4.5 billion...

Persistent organic pollutant mobility in the atmosphere

Many persistent organic pollutants (POPs) are semivolatile organic compounds (SVOCs) having vapour pressures (see Box 4.14) between 10 and 10-7Pa. At these vapour pressures SVOCs can evaporate (volatilize) from soil, water or vegetation into the atmosphere. However, as vapour pressure is temperature dependent (see Box 4.14), it follows that at lower temperatures (lower vapour pressures) Fig. 7.24 150000-year record of methane sulphonic acid (MSA) concentration, non-sea-salt-sulphate (nss-SO -)...

Persistent organic pollutants

Finally, we turn to organic pollutants as examples of exotic chemicals (i.e. those introduced by human manufacture) impacting on the global environment. Organic pollutants are considered persistent when they have a half-life (i.e. the time taken for their concentration to decrease by 50 ) of years to decades in a soil or sediment and of several days in the atmosphere. Organic pollutants persist in the environment if they are of low solubility, low volatility or resistant to degradation (see...

Radioactivity of elements

Where the number of both protons and neutrons in an atom is known we are able to identify a specific isotope of a specific element and this is termed a nuclide. Some naturally occurring elements are radioactive and specific isotopes of these elements are called radionuclides. This term implies that their nuclei are unstable and spontaneously decay, transforming the nucleus into that of a different element. Radioactive decay is written in equations that look a little like those for chemical...

Reactivity of trace substances in the atmosphere

Gases with short residence times in the atmosphere are clearly those that can be removed easily. Some of these gases are removed by being absorbed by plants or solids or into water. However, chemical reactions are the usual reason for a gas having a short residence time. What makes gases react in the atmosphere It turns out that most of the trace gases listed in Table 3.3 are not very reactive with the major components of air. In fact, the most important reactive entity in the atmosphere is a...

Saving the ozone layer

The clear links between CFCs, depletion in stratospheric 3, increased UV radiation reaching the Earth's surface and possible increased incidence of skin cancer in humans have not escaped the media, who have been able, at times during the 1970s and 1980s, to capture the imagination of the general public. It is probably correct that the CFC issue aroused immediate concern because its cause was apparently obvious in the shape of the aerosol can Although it is true that aerosol propellant was only...

Scavenged behaviour

Elements that are highly particle-reactive, characterized by large z r ratios (see Section 5.2), often have vertical profiles with surface maxima and decreasing concentrations with depth aluminium (Al) Table 6.9 Concentrations of nutrients and metals in deep (> 3000m) water in the North Atlantic and North Pacific, together with estimated oceanic residence times. Table 6.9 Concentrations of nutrients and metals in deep (> 3000m) water in the North Atlantic and North Pacific, together with...

Steady state or equilibrium

Let us look at an individual trace gas in the atmosphere. We will take methane (CH4), not an especially reactive gas, as an illustration. It is present in the atmosphere at about 1.7 ppm (Box 3.1). Methane could be imagined to react with O2 in the following way CH4(g) + 2O2(g) CO2(g) + 2H2O(g) eqn. 3.2 The reaction can be represented as an equilibrium situation (Box 3.2) and described by the conventional equation which can be written in terms of pressure (Box 3.1) The equilibrium constant (K)...

Stratospheric ozone formation and destruction

The formation of ozone is a photochemical process that uses the energy involved in light. The shorter the wavelength of light, the larger the amount of energy it Fig. 3.6 Mean October levels of total ozone above Halley Bay (76 S), Antarctica, since 1957. The 1986 value is anomalous due to deformation of the ozone hole, which left Halley Bay temporarily outside the circumpolar vortex (a tight, self-contained wind system). Dobson units represent the thickness of the ozone layer at sealevel...

The atmospheric record

The best place to start our examination is in the atmosphere, where the observational record is most complete and historical changes are best documented. Figure 7.1 shows values of the atmospheric concentration of CO2 measured at Mauna Loa (Hawaii) and the South Pole from the late 1950s until the end of the 20th century. It indicates that over this period there was a clear increase in atmospheric CO2 and that this was a worldwide phenomenon. The rate of increase varied somewhat from year to...

The chemistry of continental solids

4.1 The terrestrial environment, crust and material cycling 66 4.2 The structure of silicate minerals 70 4.2.1 Coordination of ions and the radius ratio rule 70 4.2.2 The construction of silicate minerals 73 4.2.3 Structural organization in silicate minerals 73 4.4 Mechanisms of chemical weathering 77 4.4.4 Weathering of complex silicate minerals 84 4.5.1 One to one clay mineral structure 88 4.5.2 Two to one clay mineral structure 88 4.6.1 Parent (bedrock) material (p) 94 4.6.5 Influence of...

The chemistry of continental waters 141

5.3 Water chemistry and weathering regimes 145 5.3.1 Alkalinity, dissolved inorganic carbon and pH buffering 151 5.4 Aluminium solubility and acidity 155 5.4.1 Acidification from atmospheric inputs 156 5.4.3 Recognizing acidification from sulphate data - ternary diagrams 159 5.5.1 Nutrients and eutrophication 163 5.6 Heavy metal contamination 170 5.6.1 Mercury contamination from gold mining 170 5.7 Contamination of groundwater 174 5.7.1 Anthropogenic contamination of groundwater 176 5.7.2...

The effects of elevated carbon dioxide levels on global temperature and other properties

So far we have examined the global cycling of carbon without paying attention to the role CO2 plays in the Earth's climate. Although CO2 is a minor component of the atmosphere (see Section 3.2), it plays a vital role in the Earth's radiation balance and hence in controlling the climate. This is illustrated in Fig. 7.12a, which shows the wavelength emission spectrum of the Sun and the Earth, at their effective radiating temperatures of about 5700 C and -23 C respectively. Fig. 7.12 (a) Black...

The role of iron as a nutrient in the oceans

Although abundant in the Earth's crust (see Fig. 1.3), iron is present in seawater at very low concentrations (about 1 nmol l-1or less) because the thermodynami-cally stable Fe(III) species is both insoluble (see Fig. 5.2) and particle reactive, being a highly charged small ion (Section 6.5.5). Despite this, iron is an essential component for a number of life-supporting enzyme systems including those involved in photosynthesis and nitrogen fixation. It may appear surprising that phytoplankton...

The terrestrial environment crust and material cycling

Terrestrial environments consist of solid (rocks, sediments and soils), liquid (rivers, lakes and groundwater) and biological (plants and animals) components. The chemistry of terrestrial environments is dominated by reactions between the Earth's crust and fluids in the hydrosphere and atmosphere. The terrestrial environment is built on continental crust, a huge reservoir of igneous and metamorphic rock (mass of continental crust 23.6 X 1024g). This rock, often called crystalline basement,...

Two to one clay mineral structure

The other important structural arrangement is a 2 1 structure, comprising an octahedral layer, sandwiched between two tetrahedral sheets with apical oxygens pointing inward on each side of the octahedral sheet (Fig. 4.11). The mutual sharing of two layers of apical oxygens in the octahedral sheets implies a higher oxygen OH ratio in the structure of the 2 1 vs. the 1 1 octahedral sheets. All of the other clay mineral groups share this structure, the most important being the Fig. 4.8 Schematic...

Water chemistry and weathering regimes

Comparison of dissolved major ion compositions in four large rivers draining very different crustal areas (Table 5.2) shows the dominance of calcium (Ca), magnesium (Mg), sodium (Na) and potassium (K). Overall, however, the chemistry of each river is different and weathering regimes control most of these variations. The dissolved ion composition of freshwater depends upon 1 the varying composition of rainfall and atmospheric dry deposition 2 the modification of atmospheric inputs by...

Why study globalscale environmental chemistry

In previous chapters of this book the chemistry of the atmosphere, oceans and land has been dealt with largely on an individual basis. Using a steady-state model (see Section 3.3), we can envisage each of these environments as a reservoir. In each chapter the cycling of chemicals has been discussed, together with their transformations within the reservoir. Where relevant, some attention has been paid to inputs and outputs into or out of that reservoir from or to adjacent ones. By contrast, the...

Wider controls on soil and clay mineral formation

In an average upper-crustal granodiorite, it is mainly feldspars that weather to form clay minerals (eqns. 4.13 & 4.14). Since feldspars are framework silicates, the formation of clay minerals (sheet silicates) must involve an intermediate step. This step is not at all well understood although it has been proposed that fulvic acids, from the decay of organic matter in soil, may react with aluminium to form a soluble aluminium-fulvic acid complex, with aluminium in six-fold coordination. This...

FeSS S2O2aq FeS2S SOeqn 616

The sulphite (SO2-) is subsequently oxidized to SO4-. Sedimentary pyrite, formed as a byproduct of sulphate reduction in marine sediments, is a major sink for seawater SO4-. The presence of pyrite in ancient marine sediments shows that SO42- reduction has occurred for hundreds of millions of years. On a geological timescale, removal of SO4- from seawater by sedimentary pyrite formation is thought to be about equal to that removed by evaporite deposition (Section 6.4.2). Compilations of pyrite...

Contamination of groundwater

Although aspects of groundwater chemistry have been discussed elsewhere in this chapter, this section highlights issues relating to the contamination of ground-water. Groundwater is critically important to humans since it is a major source of drinking water. For example, in the USA over 50 of the population rely on groundwater as a source of drinking water. Groundwater quality is therefore very important and, in most developed countries, water must conform to certain standards for human...

The sulphur cycle and atmospheric acidity

If CO2 were the only atmospheric gas controlling the acidity of rain, then the pH of rainwater would be close to 5.6 (see Box 3.7). However, most pH measurements of rainwater fall below this value, indicating other sources of acidity. Much of this 'extra' acidity arises from the sulphur cycle, as shown in Fig. 7.18. Only two major routes give rise to the sulphur acidity. One is the burning of fossil fuels to produce the acidic gas SO2. The other is the production of the gas DMS by marine...

London smogprimary pollution

Urban pollution is largely the product of combustion processes. In ancient times cities such as Imperial Rome experienced pollution problems due to wood smoke. However, it was the transition to fossil fuel burning that caused the rapid development of air pollution problems. The inhabitants of London have burnt coal since the 13 th century. Concern and attempts to regulate coal burning began almost immediately, as there was a perceptible and rather strange smell associated with it. Medieval...

The global budget of natural and anthropogenic carbon dioxide

We now synthesize much of the knowledge outlined in previous sections on the global budget of CO2. Firstly, the relative sizes of the natural reservoirs are considered and then the natural flows between them, followed by how anthropogenic CO2 partitions between the boxes. Finally, likely future levels of atmospheric CO2 are discussed in terms of possible scenarios of fossil fuel consumption. A simplified version of the carbon cycle is given in Fig. 7.9. By far the largest reservoir is in marine...

Box 65 Abiological precipitation of calcium carbonate

Where a skeletal source cannot be identified, calcium carbonate (CaCO3) grains and finegrained muds may be of abiological origin. The most famous occurrences occur in shallow, warm, saline waters of the Bahamas and the Arabian Gulf. In these areas two distinctive morphologies are present, ooids and needle muds (Fig. 1). aragonite* crystals around a nucleus, usually a shell fragment or pellet. Successive layers of aragonite precipitation build up a concentric structure, which may vary in size...

Box 35 The pH scale

The acidity of aqueous solutions is frequently described in terms of the pH scale. Acids (Box 3.3) give rise to hydrogen ions (H+) in solution and the pH value of such a solution is defined We can write a similar relationship identifying pOH However, pH is related to pOH through the equilibrium describing the dissociation of water H2O H+ + OH-, i.e. Kw 10-14 aH+ . aOH- It is important to notice that this is a logarithmic scale, so it is not appropriate to average pH values of solutions...

Soil structure and classification

As a result of the various factors and processes outlined in Sections 4.6.1-4.6.5, over time soils develop stable and diagnostic features, many of which are recog nizable in the field. These features, particularly specific layers called 'soil horizons', are the basis for soil classification. An idealized soil profile, i.e. a vertical section, is shown in Fig. 4.21. Soil horizons are described using an internationally agreed system of abbreviations that are shown on Fig. 4.21 and used in the...