Encyclopedia of Energy Volume I (Encyclopedia of Energy Series)

858 Pages·2004·12.935 MB·English

by  Robert U Ayres, Robert Costanza, Jose Goldemberg, Marija D Ilic, Eberhard Jochem, Robert Kaufmann, Amory B Lovins, Mohan Munasinghe, R K Pachauri, Claudia Sheinbaum Pardo, Per Peterson, Lee Schipper, Margaret Slade, Vaclav Smil, Ernst Worrell, Cutler J. Cleveland

PREFACE
The history of human culture can be viewed as the The study of energy has played a pivotal role in
progressive development of new energy sources and understandingthecreationoftheuniverse,theorigin
their associated conversion technologies. Advances of life, the evolution of human civilization and
in our understanding of energy have produced culture, economic growth and the rise of living
unparalleled transformations of society, as exempli- standards, war and geopolitics, and significant
fied by James Watt’s steam engine and the discovery environmental change at local, regional, and global
of oil. These transformations increased the ability of scales.
humans to exploit both additional energy and other The unique importance of energy among natural
resources, and hence to increase the comfort, long- resources makes information about all aspects of its
evity, and affluence of humans, as well as their attributes, formation, distribution, extraction, and
numbers. Energy is related to human development use an extremely valuable commodity. The Encyclo-
in three important ways: as a motor of economic pedia of Energy is designed to deliver this informa-
growth,asaprincipalsourceofenvironmentalstress, tion in a clear and comprehensive fashion. It uses an
andasaprerequisiteformeetingbasichumanneeds. integrated approach that emphasizes not only the
Significantchangesineachoftheseaspectsofhuman importance of the concept in individual disciplines
existence are associated with changes in energy suchasphysicsandsociology,butalsohowenergyis
sources, beginning with the discovery of fire, the used to bridge seemingly disparate fields, such as
advent of agriculture and animal husbandry, and, ecology and economics. As such, this Encyclopedia
ultimately, the development of hydrocarbon and provides the first comprehensive, organized body of
nuclear fuels. The eventual economic depletion of knowledgeforwhatiscertaintocontinueasamajor
fossil fuels will drive another major energy transi- area of scientific study in the 21st century. It is
tion; geopolitical forces and environmental impera- designed to appeal to a wide audience including
tivessuchasclimatechangemaydrivethistransition undergraduate and graduate students, teachers,
faster than hydrocarbon depletion would have by academics, and research scientists who study energy,
itself. There is a diverse palette of alternatives to as well as business corporations, professional firms,
meetourenergyneeds,includinganewgenerationof government agencies, foundations, and other groups
nuclear power, unconventional sources of hydrocar- whose activities relate to energy.
bons,myriadsolartechnologies,hydrogen,andmore Comprehensive and interdisciplinary are two
efficient energy end use. Each alternative has a words I use to describe the Encyclopedia. It has the
different combination of economic, political, tech- comprehensive coverage one would expect: forms
nological, social, and environmental attributes. of energy, thermodynamics, electricity generation,
Energyisthecommonlinkbetweenthelivingand climate change, energy storage, energy sources, the
non-living realms of the universe, and thus provides demandforenergy,andsoon.Whatmakesthiswork
an organizing intellectual theme for diverse disci- unique,however,isitsbreadthofcoverage,including
plines. Formalization of the concept of energy and insights from history, society, anthropology, public
identification of the laws governing its use by 19th policy,internationalrelations,humanandecosystem
centuryphysicalscientistssuchasMayerandCarnot health, economics, technology, physics, geology,
are cornerstones of modern science and engineering. ecology, business management, environmental
xxxi
xxxii
Preface
science, and engineering. The coverage and integra- asanuncannycombinationofvision,enthusiasm,and
tion of the social sciences is a unique feature. energyfortheproject.IoweChrisagreatdealforhis
The interdisciplinary approach is employed in the insightandprofessionalism.Ispentcountlesshourson
treatmentofimportantsubjects.Inthecaseofoil,as thephonewithRobertMatsumura,whowastheglue
one example, there are entries on the history of oil, that held the project together. Chris and Robert were
the history of OPEC, the history of oil prices, oil ably assisted by outstanding Academic Press/Elsevier
price volatility, the formation of oil and gas, the staff,especiallyNickPanissidi,JoannaDinsmore,and
distribution of oil resources, oil exploration and Mike Early. Clare Marl and her team put together a
drilling, offshore oil, occupational hazards in the oil highly effective and creative marketing plan.
industry,oilrefining,energypolicyintheoilindustry, At the next stage, the Editorial Board was
the geopolitics of oil, oil spills, oil transportation, invaluable in shaping the coverage and identifying
public lands and oil development, social impacts of authors. The Board is an outstanding collection of
oil and gas development, gasoline additives and scholars from the natural, social, and engineering
public health, and the environmental impact of the sciences who are recognized leaders in their fields of
Persian Gulf War. Other subjects are treated in a research.Theyhelpedassembleanequallyimpressive
similar way. group of authors from every discipline and who
This has been a massive and extremely satisfying represent universities, government agencies, national
effort. As with any work of this scale, many people laboratories, consulting firms, think tanks, corpora-
have contributed at every step of the process, tions, and nongovernmental organizations. I am
including the staff of Academic Press/Elsevier. The especially proud of the international scope of the
project began through the encouragement of Frank authors: more than 400 authors from 40 nations are
Cynar and David Packer, with Frank helping to represented from every continent and every stage of
successfully launch the initiative. Henri van Dorssen development.Toallofthese,Iextendmythanksand
skillfully guided the project through its completion. congratulations.
Hewas especiallyhelpful with integratingthe project
formulation, production, and marketing aspects of Cutler Cleveland
the project. Chris Morris was with the project Boston University
throughout, and displayed what I can only describe Boston, Massachusetts, United States
FOREWORD
Energy generation and use are strongly linked to all projected carbon emissions to levels below the
elements of sustainable development: economic, present.
social, and environmental. The history of human Dependence on imported fuels leaves many
development rests on the availability and use of countries vulnerable to disruption in supply, which
energy, the transformation from the early use of fire might pose physical hardships and economic bur-
andanimalpowerthatimprovedlives,tothepresent dens;theweightoffossilfuelimportsonthebalance
world with use of electricity and clean fuels for a of payments is unbearable for many poorer coun-
multitude of purposes. This progress built on basic tries. The present energy system of countries heavily
scientific discoveries, such as electromagnetism and dependent on fossil fuels geographically concen-
theinventionsoftechnologiessuchassteamengines, trated in a few regions of the world adds security
light bulbs, and automobiles. of supply aspects.
It is thus abundantly clear that access to afford- From the issues indicated here it is clear that
able energy is fundamental to human activities, major changes are required in energy system devel-
development, and economic growth. Without access opmentworldwide.Atafirstglance,thereappearsto
to electricity and clean fuels, people’s opportunities be many conflicting objectives. For example, is it
are significantly constrained. However, it is really possible to sustain poverty alleviation and economic
energy services, not energy per se that matters. Yet, growth while reducing GHG emissions? Can urban
today some 2 billion people lack access to modern areas and transport expand while improving air
energy carriers. quality? What would be the preferable trade-offs?
In addition to the great benefits, the generation, Finding ways to expand energy services while
transportation, and use of energy carriers unfortu- simultaneously addressing the environmental im-
nately come with undesired effects. The environ- pacts associated with energy use represents a critical
mental impacts are multifaceted and serious, challenge to humanity.
althoughmostlylessevident.Emissionsofsuspended What are the options? Looking at physical
fine particles and precursors of acid deposition resources, one finds they are abundant. Fossil fuels
contribute to local and regional air pollution and will be able to provide the energy carriers that the
ecosystem degradation. Human health is threatened world is used to for hundreds of years. Renewable
by high levels of air pollution resulting from energy flows on Earth are many thousands of times
particular types of energy use at the household, larger than flows through energy markets. Therefore,
community, and regional levels. there are no apparent constraints from a resource
Emissions of anthropogenic greenhouse gases point of view. However, the challenge is how to use
(GHG), mostly from the production and use theseresourcesinanenvironmentallyacceptableway.
of energy, are altering the atmosphere in ways The broad categories of options for using energy in
that are affecting the climate. There is new and ways that support sustainable development are (1)
stronger evidence that most of the global warming moreefficientuseofenergyinallsectors,especiallyat
observed over the last 50 years is attributable the point of end use, (2) increased use of renewable
to human activities. Stabilization of GHG in the energy sources, and (3) accelerated development and
atmosphere will require a major reduction in the deploymentofnewandadvancedenergytechnologies,
xxvii
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Foreword
including next-generation fossil fuel technologies that protect important public benefits, including the
produce near-zero harmful emissions. Technologies following:
are available in these areas to meet the challenges of
(cid:1) Cost-based prices, including phasing out all
sustainable development. In addition, innovation
forms of permanent subsidies for conven-
provides increasing opportunities.
tional energy (now on the order of $250
Analysis using energy scenarios indicates that it is
billion a year) and internalizing external
indeed possible to simultaneously address the sus-
environmental and health costs and benefits
tainable development objectives using the available
(nowsometimeslargerthantheprivatecosts).
natural resources and technical options presented. A
(cid:1) Removing obstacles and providing incentives,
prerequisite for achieving energy futures compatible
as needed, to encourage greater energy
with sustainable development objectives is finding
efficiency and the development and/or diffu-
ways to accelerate progress for new technologies
sion of new technologies for energy for
along the energy innovation chain, including re-
sustainable development to wider markets.
search and development, demonstration, deploy-
(cid:1) RecentpowerfailuresontheNorthAmerican
ment, and diffusion.
Eastern Seaboard, in California, London
It is significant that there already exist combina-
(United Kingdom), Sweden, and Italy illus-
tions of technologies that meet all sustainable
tratethestrongdependenceonreliablepower
development challenges at the same time. This will
networks. Power sector reform that recog-
make it easier to act locally to address pollution
nizes the unique character of electricity, and
problemsofamajorcityorcountrywhileatthesame
avoids power crises as seen in recent years, is
time mitigating climate change. Policies for energy
needed.
forsustainabledevelopmentcanbelargelymotivated
(cid:1) Reversing the trend of declining Official Devel-
by national concerns and will not have to rely only
opment Assistance and Foreign Direct Investments,
on global pressures.
especially as related to energy for sustainable
However, with present policies and conditions in
development.
the marketplaces that determine energy generation
and use such desired energy futures will not happen. This is a long list of opportunities and challenges.
Aprerequisiteforsustainabledevelopment ischange To move sufficiently in the direction of sustain-
in policies affecting energy for sustainable develop- ability will require actions by the public and the
ment. This brings a need to focus on the policy private sector, as well as other stakeholders, at
situationandunderstandincentivesanddisincentives thenational,regional,andgloballevels.Thedecisive
related to options for options for energy for issuesarenottechnologyornaturalresourcescarcity,
sustainable development. buttheinstitutions,rules,financingmechanisms,and
Policies and actions to promote energy for regulationsneededtomakemarketsworkinsupport
sustainable development would include the follow- of energy for sustainable development. A number of
ing: countries, including Spain, Germany, and Brazil, as
wellassomestatesintheUnitedStateshaveadopted
(cid:1) Developing capacity among all stakeholders in successful laws and regulations designed to increase
all countries, especially in the public sector, to the use of renewable energy sources. Some regions,
address issues related to energy for sustainable including Latin America and the European Union,
development. have set targets for increased use of renewable
(cid:1) Adopting policies and mechanisms to increase energy. However, much remains to be done.
access to energy services through modern fuels and Energy was indeed one of the most intensely
electricity for the 2 billion without. debated issues at the United Nations World Summit
(cid:1) Advancing innovation, with balanced emphasis on Sustainable Development (WSSD), held in Johan-
on all steps of the innovation chain: research and nesburg,South Africa, in August/September, 2002. In
development, demonstrations, cost buy-down, and the end, agreement was reached on a text that
wide dissemination. significantly advances the attention given to energy
(cid:1) Setting appropriate market framework condi- in the context of sustainable development. This was
tions (including continued market reform, consistent in fact the first time agreements could be reached
regulatory measures, and targeted policies) to en- on energy at the world level! These develop-
couragecompetitivenessinenergymarkets,toreduce ments followed years of efforts to focus on energy
total cost of energy services to end-users, and to as an instrument for sustainable development that
xxix
Foreword
intensified after the United Nations Conference on energy, a total of 39 partnerships were presented to
Environment and Development in 1992. theUnitedNationsSecretariatforWSSDtopromote
The United Nations General Assembly adopted programs on energy forsustainable development, 23
theMillenniumDevelopmentGoals(MDG)in2000. with energy as a central focus and 16 with a
These goals are set in areas such as extreme considerable impact on energy. These partnerships
poverty and hunger, universal primary education, includedmostprominentlytheDESA-ledCleanFuels
gender equality and empowerment of women, and Transport Initiative, the UNDP/World Bank-led
child mortality, maternal health, HIV/AIDS, malaria Global Village Energy Partnership (GVEP), the
and other diseases, and environmental sustain- Johannesburg Renewable Energy Coalition (JREC),
ability. However, more than 2 billion people cannot the EU Partnership on Energy for Poverty Eradica-
access affordable energy services, based on the tion and Sustainable Development, and the UNEP-
efficient use of gaseous and liquid fuels and led Global Network on Energy for Sustainable
electricity. This constrains their opportunities for Development (GNESD).
economic development and improved living stan- With secure access to affordable and clean energy
dards.Womenandchildrensufferdisproportionately being so fundamental to sustainable development,
because of their relative dependence on traditional the publication of the Encyclopedia of Energy is
fuels. Although no explicit goal on energy was extremely timely and significant. Academics, profes-
adopted, access to energy services is a prerequisite sionals, scholars, politicians, students, and many
to achieving all of the MDGs. more will benefit tremendously from the easy access
Some governments and corporations have already to knowledge, experience, and insights that are
demonstrated that policies and measures to promote provided here.
energy solutions conducive to sustainable develop-
ment can work, and indeed work very well. The Thomas B. Johansson
renewedfocusandbroadagreementsonenergyinthe Professor and Director
JohannesburgPlanofImplementationandatthe18th International Institute for
WorldEnergyCongressarepromising.Theformation Industrial Environmental Economics
ofmanypartnershipsonenergybetweenstakeholders Lund University
at WSSD is another encouraging sign. A sustainable Lund, Sweden
future in which energy plays a major positive role in
supporting human well-being is possible! Former Director
Progressisbeingmadeonmanyfrontsinbringing Energy and Atmosphere Programme
new technologies to the market, and to widening United Nations Development Programme
access to modern forms of energy. In relation to New York, United States
Acid Deposition and Energy Use
A
JAN WILLEM ERISMAN
EnergyResearch Centre of theNetherlands
Petten, TheNetherlands
pollutant Any substance in the wrong place at the wrong
1. Introduction time is a pollutant. Atmospheric pollution may be
definedasthepresenceofsubstancesintheatmosphere,
2. Acid Deposition,ItsEffects, andCriticalLoads
resulting from man-made activities or from natural
3. Processes inthe CausalChain:Emission,Transport,
processes, causing effects to manandthe environment.
andDeposition
4. Emissions from EnergyUse
5. Abatement andTrendsinEmission
Acid deposition originates largely from man-made
6. Acid Deposition
emissions of three gases: sulfur dioxide (SO ),
7. Benefits and Recovery ofEcosystems 2
nitrogen oxides (NO ), and ammonia (NH ). It
8. FutureAbatement x 3
damages acid-sensitive freshwater systems, forests,
9. Conclusion
soils, and natural ecosystems in large areas of
Europe, the United States, and Asia. Effects include
defoliation and reduced vitality of trees; declining
fish stocks and decreasing diversity of other aquatic
Glossary animals in acid-sensitive lakes, rivers, and streams;
acid deposition The removal of acidic or acidifying and changes in soil chemistry. Cultural heritage is
componentsfromtheatmospherebyprecipitation(rain, also damaged, such as limestone and marble build-
cloud droplets, fog, snow, or hail); also known as acid ings, monuments, and stained-glass windows. De-
rainoracid precipitation. position of nitrogen compounds also causes
acidification The generation of more hydrogen ions (Hþ) eutrophication effects in terrestrial and marine
thanhydroxideions(OH(cid:2))sothatthepHbecomesless ecosystems. The combination of acidification and
than7.
eutrophication increases the acidification effects.
criticallevel Themaximumpollutantconcentrationapart
Energy contributes approximately 82, 59, and
of the environment can be exposed to without
0.1% to the global emissions of SO , NO , and
significantharmfuleffects. 2 x
NH , respectively. Measures to reduce acid deposi-
critical load The maximum amount of pollutant deposi- 3
tion have led to controls of emissions in the United
tion a part of the environment can tolerate without
significantharmfuleffects. States and Europe. Sulfur emissions were reduced
deposition Can be either wet or dry. In dry deposition, 18% between 1990 and 1998 in the United States
material is removed from the atmosphere by contact and 41% in Europe during the same period. At the
with a surface. In wet deposition, material is removed sametime,emissionsinAsiaincreased43%.Inareas
fromthe atmosphere byprecipitation. of the world in which emissions have decreased, the
emissions Thereleaseofprimarypollutantsdirectlytothe effectshavedecreased;mostnotably,lakeacidityhas
atmosphere by processes such as combustion and also
decreased due to a decrease in sulfur emissions,
bynatural processes.
resulting in lower sulfate and acid concentrations.
eutrophication An increase of the amount of nutrients in
However,systemswithalongresponsetimehavenot
waters orsoils.
seen improvement yet and very limited recovery has
nitrification Theconversionofammoniumions(NHþ)to
4
nitrate (NO(cid:2)). also been observed. Emissions should therefore be
3
nonlinearity The observed nonlinear relationship between further reduced and sustainable levels should be
reductions in primary emissions and in pollutant maintained to decrease the effects and to see
deposition. recovery. This will require drastic changes in our
EncyclopediaofEnergy,Volume1.r2004ElsevierInc.Allrightsreserved. 1
2
AcidDepositionandEnergyUse
energy consumption and the switch to sustainable 400 16000
energy sources. Before renewable energy sources can Primary energy consumption, EJ
fzseteauihenmnmlrovdfioieuislr-.sllNeodiTomnaOnhmiblssexaesebrinmeogetmnecaodalisofsputonsiasimsceeorsotinptslihsatonf.-icufestfeWsowfslesuuhiacclrmetrlhienvreuenesassateutdwrabldgtraewyrtyieiinansmniysgsdeepeedtlwdtcoehrsmiaea,trthaetetsndhteStuhdeseOceidifeun2f.sesCTeaSraemOOhnnoide22stf y consumption and share 332211505050000000 PESSlhoheapacrurteerliassc t ioitooyffn gPP, eEEmnCCeil l roicaoiotln iaoalnn (,d% T g)Wash (%) 111864420000000000000000000opulation and electricitygeneration (TWh)
NOx emissions, an energy penalty compensates for nerg 50 2000 P
the emission reductions. E
0 0
1880 1900 1920 1940 1960 1980 2000 2020
Year
1. INTRODUCTION
FIGURE1 Theworldwideuseoffossilfuelsinmillionsoftons
peryear.AdaptedfromSmil(2000).
The alarm regarding the increasing acidification of
precipitation in Europe and eastern North America
was first sounded in the 1960s. Since then, most
attention has focused on acid rain’s effects, estab- sources has increased and has become higher than
lishedandsuspected,onlakesandstreams,withtheir the share of coal.
populations of aquatic life, and on forests, although Thefirstenvironmentalconsequencesoftheuseof
the list of concerns is far broader: It includes fossilfuelsweretheproblemsofsmokeinhousesand
contamination of groundwater, corrosion of man- urban air quality. Human health was affected by the
made structures, and, recently, deterioration of useofcoalwithhighsulfurcontent,producingsulfur
coastal waters. dioxide and carbon monoxide. The history of
Theprocessesthatconvertthegasesintoacidand London clearly shows the ever-increasing problems
wash them from the atmosphere began operating related to coal use and the struggle to abate this
long before humans started to burn large quantities pollution, culminating in the famous London smog
of fossil fuels. Sulfur and nitrogen compounds are in1952,fromwhichthousandsofpeopledied.Inthe
also released by natural processes such as volcanism 1950sand1960s,airpollutionbecameanimportant
and the activity of soil bacteria. However, human issue but was mainly considered on the local scale.
economicactivityhasmadethereactionsvastlymore One of the abatement options was to increase the
important. They are triggered by sunlight and stack height in order to take advantage of atmo-
depend on the atmosphere’s abundant supply of spheric dispersion, leading to dilution of pollutant
oxygen and water. concentrations before humans could be exposed.
Wood was the first source for energy production. Thisformedthebasisofthetransboundarynatureof
Wood was used for the preparation of food and for acid deposition as we know it today and increased
heating.Afterthediscoveryoffossilfuelsintheform thescalefromlocaltoregionalandevencontinental.
of coal as a source of energy, it was used for heating The use of fossil fuels increased, and the pollutants
purposes. During the industrial revolution, coal, were transported to remote areas, which had very
followedbycrudeoilandlaternaturalgas,provided clean air until that time.
alargesourceofenergythatstimulatedtechnological Acid rain was first recognized as a serious
development,resultinginthereplacementofanimals environmental problem by Robert Angus Smith, an
and people in the production of goods, increased alkali inspector based in Manchester. He started a
possibilities for mobility, and the enabling of monitoring network with approximately 12 sites at
industries to process raw materials into a large which rainfall was collected and analyzed. In 1852,
variety of products. When the possibilities of energy hewroteaboutthecorrelationbetweencoalburning
production and use became apparent, the use of and acid pollution in and around the industrial
fossil fuels grew exponentially. Figure 1 provides an centerofManchester.Heidentifiedthreetypesofair:
overview of the worldwide use of fossil fuels since ‘‘that with carbonate of ammonia in the fields at a
1900.Itshowsthatthetotalglobalenergyconsump- distance y that with sulphate of ammonia in the
tion is closely linked to the growth of the world’s suburbs, y and that with sulphuric acid, or acid
population. The share of oil and gas as energy sulphate,inthetown.’’In1872,hewrotethefamous
3
AcidDepositionandEnergyUse
book, Air and Rain: The Beginnings of a Chemical damage in forests. Trees showed decreased foliage
Climatology. He referred to the acidity of rain and or needles, and this damage even progressed to the
air and its effect on humans and buildings. This was point that trees would die, a phenomenon that
the beginning of acidification research, although this happenedintheborderareaofformerEastGermany,
was recognized only much later. Poland, and former Czechoslovakia. This tree die-
Aciddepositionisoneoftheoldesttransboundary back was also attributed to acidification of the soil.
environmental problems. Several components and However, exposure to increased oxidant concentra-
thus emission sources contribute to acid deposition, tionswasdeterminedtobeanothercause.Inthemid-
making it a complex problem and difficult to abate. 1980s, nitrogen deposition to terrestrial and aquatic
Itisoneofthemoststudiedenvironmentalproblems ecosystems was found to cause negative effects
and there is a large body of literature. This article through eutrophication. Acidification and eutrophi-
givesanoverviewofthestateofknowledgeofenergy cation are both caused by atmospheric deposition of
production and use and acid deposition. First, an pollutants,andthecombinationincreasestheeffects,
overview is given of acid deposition, the conse- causing too high nutrient concentrations in soil and
quences of acid deposition, and the processes groundwater. Nitrate and ammonium are beneficial,
involved. The contribution of energy is discussed evenessential,forvegetationgrowth,butintoohigh
next, and an estimate of the progress made to concentration they lead to the loss of diversity,
decrease the emissions from energy sources is given. especiallyinoligotrophicecosystems(i.e.,ecosystems
Finally, future options to decrease acid deposition adapted to low nutrient availability). This problem
and the options for decreasing energy emissions are has mainly been encountered in central and north-
discussed. western Europe.
The effects of acid deposition include changes in
terrestrial and aquatic ecosystems showing acidifica-
tion of soils, shifts in plant community composition,
2. ACID DEPOSITION, ITS EFFECTS,
loss of species diversity, forest damage, water
AND CRITICAL LOADS acidification and loss of fish populations, reduction
in growth yield of sensitive agricultural crops, and
Acid deposition is the deposition of air pollutants to damage to cultural heritage and to building materi-
ecosystems leading to acidification and eutrophica- als. The common factor for all these effects is that
tion,whichcausenegativeeffectsintheseecosystems. pollutants, or their precursors, are emitted, trans-
The components contributing to acid deposition are ported in the atmosphere, and deposited by way of
sulfur compounds (SO and SO ), oxidized nitrogen precipitation(wetdeposition)orasgasesorparticles
2 4
compounds (NO, NO , HNO , HNO , and NO ), (dry deposition). In some cases, acid deposition
2 2 3 3
and reduced nitrogen compounds (NH and NH ). occurs 1000km or more from where the responsible
3 4
Some rain is naturally acidic because of the carbon emissions were generated.
dioxide (CO ) in air that dissolves with rain water Ifdepositionexceedssustainablelevels,effectscan
2
and forms a weak acid. This kind of acid is actually occurdependingonthedurationoftheexposureand
beneficialbecauseithelpsdissolvemineralsinthesoil the level of exceedance. Sustainable levels can be
that both plants and animals need. Ammonia acts as represented by critical loads and critical levels. The
a base in the atmosphere, neutralizing nitric and critical load is formally defined by the United
sulfuricacid,butinsoilammoniaitcanbeconverted NationsEconomicCommissionforEurope(UNECE)
by microorganisms to nitric acid, producing addi- as ‘‘a quantitative estimate of exposure to one or
tional acid in the process. more pollutants below which significant harmful
The first sign of the effects of acid deposition was effects on sensitive elements of the environment do
the loss of fish populations in Canadian, Scandina- not occur according to present knowledge.’’ This
vian, and U.S. lakes in the early 1960s. It was found definition can be applied to a wide range of
thatthewaterinthelakeswasacidifiedtoapointat phenomena and not merely acid rain. Any process
whichfisheggsnolongerproducedyoungspecimens. in which damage will occur if depositions exceed
This was caused by acid deposition; precipitation natural sink processes has a critical load set by
had introduced so much acid in the lakes that pH those sink processes. The concept of critical loads or
levels had declined below the critical limit for egg levels has been used to provide a scientific basis for
hatching.Afewyearslater,reportsfromCanada,the the incorporation of environmental impacts in the
United States, and Germany indicated unusual developmentofnationalandinternationalpoliciesto
4
AcidDepositionandEnergyUse
control transboundary air pollutants, within the contain sulfur compounds, which are emitted into
framework of the UNECE Convention on the the atmosphere as SO after combustion. Oxidized
2
ControlofTransboundaryAirPollution.Theconcept nitrogen has several sources but is formed mainly by
isbasedontheprecautionaryprinciple:Criticalloads combustion processes in which fuel N is oxidized or
andlevelsaresettopreventanylong-termdamageto atmospheric N is oxidized at high temperatures.
2
themostsensitiveknownelementsofanyecosystem. These processes are relevant for industries, traffic,
The critical loads approach is an example of an and energy production. Among the other sources of
effects-based approach to pollution control, which oxidized nitrogen, soils are most important. Ammo-
considers that the impact of deposited material niaismainlyemittedfromagriculturalsources.Fossil
depends on where it lands. Similar industrial plants fuels seem less important for ammonia than for the
may have different pollution impacts depending on other two pollutants. Through the use of fertilizer,
thedifferentcapacitiesofthereceivingenvironments which is produced from natural gas, there is a link
to absorb, buffer, or tolerate pollutant loads. The withenergy.Indirectly,theincreasedenergyusefrom
policy goal with effects-based strategies is ultimately fossil fuels to produce fertilizer has increased nitro-
to ensure that the abatement on emissions from all gen emissions from agriculture and contributed to
plants is adequate so that no absorptive capacities, acidification. Energy use first increased mobility.
nor air quality standards, are exceeded. Food is therefore not necessarily produced in the
area where it is consumed. Furthermore, relatively
cheap nutrient resources (animal feed) are trans-
3. PROCESSES IN THE CAUSAL portedfromonecontinenttoanother,wheretheyare
concentrated in intensive livestock breeding areas.
CHAIN: EMISSION, TRANSPORT,
Also, fossil fuels, first in the form of coal but now
AND DEPOSITION
mainlyfromnaturalgas,providethebasistoproduce
fertilizers, which are used to produce the food
The causal chain represents the sequence of emis-
necessary to feed the ever-growing population
sions into the atmosphere, transport and chemical
throughout the world and to fulfill the need for the
reactions,depositiontotheearthsurface,andcycling
growing demands for more luxurious food.
within the ecosystems until eventually the compo-
Base cations play an important role because they
nents are fixed or transformed in a form having no
can neutralize acids in the atmosphere and the soil,
effects.ThiscausalchainisshowninFig.2.Afterthe
limiting the effect of acid deposition. On the other
causal chain is understood and parameterized in
hand, base cations contribute to the particle concen-
models, it can be used to assess the possibilities for
trations in the atmosphere, affecting human health
reducing the effects.
when inhaled. Sources of base cations are energy
production, agricultural practices, and road dust.
3.1 Emission
3.2 Transport and Deposition
Theuseoffossilfuelsforenergyproductionisoneof
the main causes of acid deposition. Fossil fuels The sulfur compounds are converted to sulfuric acid
and NO to nitric acid, and ammonia reacts with
x
theseacidstoformammoniumsalts.Bothprecursors
SO N2,H N3 Ox SSOO422, −N NOOx 3N−NHH3 4+ SSOO422−, NNOO3x− NNHH34 + SO4S2−O N2O, N3O−NxH N4H+3 (nSiOtri2c,aNciOd,x,anadndamNmHo3n)iuanmdsaplrtosd)ucactnsb(esutlrfaunriscpoarctiedd,
Rain over long distances (up to 1500km), depending on
Wet and dry meteorological conditions, speed of conversion, and
NH3 NOx SO2 Dry teW Wet d Dryeposition rSeOmo,vNalOby,daepnodsitNioHn p,robceehsasvees. Tdihfefegreansetlsyeminitttehde,
2 x 3
Emissions atmosphere. The residence time of NH3 is relatively
short because it is emitted at low level (near the
Dry teW ground), it converts quickly to NHþ, and the dry
4
deposition rate is fairly high. NH is transported
3
100–500km. The horizontal and vertical concentra-
FIGURE 2 Emission, transport, and deposition of acidifying tiongradientsaresteep,soconcentrationsanddepo-
pollutants. sitions can vary significantly over small distances.
5
AcidDepositionandEnergyUse
This means that a large proportion of the NH physical and chemical processes in the atmosphere,
3
emitted in The Netherlands is also deposited within andthereceptortype(landuse,roughness,moisture
thiscountry.OnceconvertedintoNHþ,whichhasa status, degree of stomatal opening of vegetation,
4
much lower rate of deposition, the transport snow cover, etc.). When gases and/or particles are
distances are much greater (up to 1500km). SO is depositedorabsorbeddirectlyfromtheair,wespeak
2
mainly emitted into the atmosphere by high sources of dry deposition. When they reach the surface
andcanthereforebetransportedoverlongdistances, dissolved in rain or another form of precipitation,
despiteitsrelativelyhighdepositionrate. SomeNO we refer to wet deposition. If this occurs in mist or
x
is also emitted by low sources (traffic). However, fog,itiscloud/fogdeposition.Thetotaldepositionis
becauseofitslowdepositionrateandrelativelyslow the sum of the dry, wet, and cloud/fog deposition.
conversion rate into rapidly deposited gases (HNO Throughfall is washed from the vegetation by rain
3
and HNO ), NO is transported over relatively long falling on the soil beneath the forest canopy. It is a
2 x
distances before it disappears from the atmosphere. measure of the load on the vegetation’s surface,
SO is quickly converted to sulfuric acid (H SO ) whereas the total deposition indicates the load on
2 2 4
after deposition, both in water and in soil. NO and thewholesystem(soilþvegetation).Netthroughfall
x
NH andtheirsubsequentproductscontributetothe is the difference between throughfall and wet
3
eutrophication and also the acidification of the deposition in the open field; it is a measure of the
environment as a result of conversion to nitric acid dry deposition plus cloud/fog deposition when no
(HNO ) in the air (NO ) or in the soil (NH ). exchangetakesplacewiththeforestcanopy(uptake
3 x 3
Since the three primary gases (SO , NO , and or discharge of substances through leaves, micro-
2 x
NH )canreactandbeinequilibriumwitheachother organisms, etc.).
3
and with the different reaction products in the To understand the impact of emissions on the
atmosphere, there is a strong and complex mutual effectscausedbyaciddepositionandeutrophication,
relationship. If, for example, there were no NH in thewholechainofemissions,transport,atmospheric
3
theatmosphere,SO wouldbeconvertedlessquickly conversion, dry and wet deposition, and the effects
2
to SO2(cid:2). The environment, however, would also be caused by the total deposition loads, including the
4
‘‘more acid’’so that the deposition rate of acidifying role of groundwater and soils, must be understood.
compounds would be reduced (poor solubility of Wetanddrydepositionarenotonlytheprocessesby
these compounds in acid waters). The net impact is whichpollutantsaretransportedtotheearthsurface
difficult to determine, but it is certainly true that if and humans and ecosystems are exposed to acid
the emission of one of the compounds increases or deposition and eutrophication but also play an
decreases relative to that of the others, this will also essential role in cleaning of the atmosphere. If
influencethetransportdistancesanddepositionrates removal by wet and dry deposition stopped, the
of the other compounds. This is only partly taken earth’s atmosphere would be unsuitable to sustain
into account in the scenario calculations because life in a relatively short period—on the order of a
such links have not been fully incorporated into the few months.
models. Since acidifying deposition involves different
The base cations can neutralize the acidifying substances, it is necessary to give these substances a
deposition and, after deposition to the soil, they act singledenominatorinordertoindicatethetotalload
as a buffer both in terms of neutralization and in of acidifying substances. For this purpose, the total
terms of uptake by plants and the prevention of load is expressed as potential acid, calculated as
nutrient deficiencies. This applies especially to the follows:
Mg2þ, Ca2þ, and Kþ compounds. The degree of 2SO þNO þNH ðmolHþha=yearÞ;
x y x
deposition of base cations is therefore important
in determining the critical loads that an ecosystem where SO are oxidized sulfur compounds, NO are
x y
can bear or the exceedances thereof. Thus, accurate oxidized nitrogen compounds, and NH are reduced
x
loads are also required for base cations on a local nitrogencompounds.Theconceptofpotentialacidis
scale. These estimates are not available for The used because NH is considered to be a potentially
3
Netherlands nor for Europe. acidifyingsubstance.Intheatmosphere,NH actsas
3
The nature and size of the load of acidifying abase,whichleadstotheneutralizationofacidssuch
substances on the surface depend on the character- asHNO andH SO .However,theNHþ formedin
3 2 4 4
istics of the emission sources (height and point or the soil can be converted to NO(cid:2) so that acid is still
3
diffuse source), the distance from the source, produced via bacterial conversion (nitrification)