Air Pollution and Climate ChangeTwo sides of the same coin?

AIR POLLUTION

Two sides of the same coin?

CLIMATE CHANGE&

Common Roots of Air Pollution and Climate Change1CHAPTER

2 AIR POLLUTION ANd CLIMATE CHANGE

CONTENTs FROM THE BOOK

Common Roots of Air Pollution and Climate Change

development of Greenhouse Gas and Air Pollution Emissions

Atmospheric Aerosols – Cooling and Warming of the Climate

Ozone and Methane – Climate and Environment Connected

Nitrogen Effects on Ecosystems in a Climate Change Perspective

Climate Change Modifies Air Quality

Air Pollution Interacts with Climate Change – Consequences for Human Health

Air Pollutants and Greenhouse Gases – Options and Benefits from Co-Control

Air Pollution and Climate Change – the Case for Integrated Policy from an Asian Perspective

Air Pollution and Climate Change Links – a United states Perspective

Towards a Joint strategy for Air Pollution and Climate Change

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3 PERINGE GRENNFELT

Ozone and particles are known to have a great impact on the radiation balance of the Earth and are consequently included in climate change assessments.

The atmosphere is one of the largest waste dis-posal units for modern society. For thousands of years it has handled gaseous and particulate waste from combustion and other human ac-tivities. It has also been found to have great self-cleaning capacity. Most air pollutants dis-appear from the atmosphere within a few days after being emitted through deposition to the ground, in particular through washout by pre-cipitation. Some of the less water-soluble com-pounds, such as many volatile organic com-pounds (VOCs), are converted by oxidation processes in the atmosphere to water, carbon dioxide and water-soluble compounds, which are quickly removed. It should be noted that the deposited pollutants can have significant environmental effects in terrestrial and aquatic ecosystems after they have left the atmosphere.

The cleaning capaciTy of the atmosphere is much lower for some of the emitted com-pounds. They will remain in the air far longer. They are of particular interest if, like carbon dioxide and nitrous oxide, they affect the ra-diation balance of the atmosphere and thus the temperature at the Earth’s surface. Historically we have not considered these compounds to be pollutants, since they are not directly toxic to humans, plants or other organisms. Indi-rectly they are clearly pollutants, as they occur in concentrations that adversely affect ecosys-tems, human health and welfare through their climate effects.

Some of The short-lived, toxic compounds tra-ditionally considered to be air pollutants may also affect the climate. Ozone and particles are

known to have a great impact on the radiation balance of the Earth and are consequently in-cluded in climate change assessments. It is thus not possible to unambiguously separate many compounds into distinct groups of either air pollutants or climate-influencing gases and particles. We need to consider their contribu-tion both to toxic effects and to climate change.

The reSidence Time and physical and chemical properties of a number of important air pol-lutants and greenhouse gases and particles are of particular importance in environmental risk assessment. The main compounds of signifi-cance in the present context, and their role in promoting toxic and climate change effects are shown in Table 1.1.

Air Pollution – much has been done but further control is needed Over the last 20-30 years air pollution emis-sions have declined substantially in Europe and North America due to national and co-ordinated international action. This has been particularly the case for sulphur. Substantial emission reductions for particles, nitrogen ox-ides and volatile organic compounds have also been achieved (Table 2).

Common Roots of Air Pollution and Climate Change

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4 AIR POLLUTION ANd CLIMATE CHANGE

Figure 1.1 The atmosphere is attractive to look at. In addition, it is critical to human existence in several ways. For example, it provides us with oxygen to breathe and supports our crops with rainfall. It has also become an enormous waste disposal unit for modern society, for both traditional air pollutants and greenhouse gases. The capacity of the atmosphere to handle emissions of various kinds is limited. Exceeding this level has led to environmental threats from climate change and the toxic effects of pollutants.

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Table 1.1 Residence times in the atmosphere, toxic properties and effect on climate change of different gases and particle types.

Compound Residence time Toxic properties Climate change properties

Carbon dioxide 150 years acidification of sea waters, affects photosynthesis

climate gas, long residence time

Nitrous oxide 110 years destruction of the stratospheric ozone layer

climate gas, long residence time

Methane 10 years precursor of ground-level ozone climate gas, intermediate residence time

Ozone 1 month adverse effects on health and vegetation

climate gas, short residence time

Sulphur dioxide 1 week acidification, health effects sulphate particles suppressing global warming

Soot 1 week health effects soot and black particles increase global warming

Nitrogen oxides 1 week precursor of ground-level ozone, acidification, eutrophication

nitrate particles may suppress global warming

Ammonia <1 week acidification, eutrophication ammonium particles may suppress global warming

The forceS driving European emission reduc-tions have included both health and ecosys-tem effects. In Europe the severe air pollution situations during wintertime inversions, with high levels of soot and sulphur dioxide, have prompted emission reductions, mainly since the severe smog episode in London in Decem-ber 1952, which resulted in a large number of premature deaths. The early control measures were directed towards emission reductions, but also to a large extent towards higher stacks. Emitting pollutants at greater height improves ground-level air quality. Pollutants are emitted above the normally occurring inversion levels, and the time for dilution until the plume reach-es the ground is increased.

in norTh america, the primary force driving air pollution control was the occurrence of photochemical smog, with the greatest prob-lems occurring on the American west coast, in particular in the Los Angeles Basin. The emission reductions to control photochemi-cal smog were directed towards nitrogen ox-ides and volatile organic compounds, and the policy has been successful in reducing peak ozone concentrations in large urban areas. In general, these early air pollution policies were

national, with no or limited international co-ordination.

in The laTe 1960s, several observations altered the perception of air pollution as a local phe-nomenon. One was the accumulating evidence of long-range transport of air pollution, that high concentrations of particular pollutants could be observed far away from the source areas and that pollutants emitted in one coun-try could contribute to adverse effects in other countries. There were also several observations of severe ecosystem damage, in particular acid-ification of surface waters, due to long-range transported air pollution. The transbound-ary transport of these pollutants made it clear that there was a need for coordinated interna-tional efforts to control emissions. These in-sights provided the basis for the Convention on Long-Range Transboundary Air Pollution that was signed in 1979. Eight protocols have been signed and ratified under the Convention.

european emiSSionS of sulphur have been substantially reduced since 1980. Today, they are back to levels comparable to those at the end of the 19th century. Many countries have reduced their emissions of sulphur dioxide by

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6 AIR POLLUTION ANd CLIMATE CHANGE

2004

2000

1995

1990

1985

1980

1975

1970

1965

1960

1955

1950

1945

1940

1935

1930

1925

1920

1915

1910

1900

1905

1895

1890

1885

1880

60

50

40

30

20

10

0

Tg SO2

Table 1.2 Emissions (Tg /year) of sulphur dioxide, nitrogen oxides and ammonia 1990-2006 in the United States and Europe (EU27). Data from USEPA and EEA.

Compound US 1990 US 2006 Trend % EU27 1990 EU27 2006 Trend %

sulphur dioxide, sO2

23,077 14,714 -36 27,323 8,284 -70

Nitrogen oxides, NOx

25,527 17,694 -23 17,136 11,294 -34

Ammonia, NH3

4,320 4,135 -4 5,120 4,094 -20

more than 90% from peak levels. As shown in Table 1.2, within the European Union (EU27), sulphur emissions were reduced by 70% be-tween 1990 and 2006. US sulphur emissions have also been substantially reduced, but to a lesser extent, by about 36% over the same time period. It is evident from Table 1.2 that emissions of nitrogen oxides and ammonia have also been reduced, although not to the same extent as sulphur dioxide.

Ground-level ozone – from local to global Ground-level ozone is one example of how a local problem has grown in scale as a result of global industrialisation and the interactions of emissions over large geographical areas. When photochemical smog, of which ground-level ozone is the main component, was first recog-nised in southern California after World War II, it was considered to be a local phenomenon unique to the Los Angeles Basin. The acute effects on humans and plants could be attrib-uted to large emissions of nitrogen oxides and volatile organic compounds under conditions that strongly promoted photochemical ozone production: abundant solar radiation and lim-ited air mixing. Many chemical reactions in the atmosphere are dependent on sunlight and are consequently termed photochemical. Even though photochemical problems were observed in other places, the problem was considered to be amenable to solution by local measures.

Figure 1.2 Emissions of sulphur dioxide in Europe over the period 1880-2005. Source: Vestreng et al, Atmospheric Chemistry and Physics 2007.

Many chemical reactions in the atmosphere are dependent on sunlight and are consequently ter-med photochemical. Even though photochemical problems were ob-served in other places, the problem was considered to be amenable to solution by local measures.

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in The 1970s, alongside the development of local control strategies in California, it was realised that the problem was not local, but regional or even continental. Ozone episodes were ob-served at the same time over large areas of both Europe and North America in connec-tion with stable summer high-pressure cells. These ozone episodes formed the basis for the development of continentally-directed control strategies in Europe. Furthermore, it was re-alised that superimposed on these continental episodes there was a continuously rising back-ground concentration of ozone over the entire Northern Hemisphere.

air polluTion and climate change issues con-verge in the increasing background concentra-tions of ozone. Despite mostly not exceeding any air quality standards, the rising back-ground level of ozone will probably lead to reduced plant growth as well as adverse effects on human health. In addition, a higher back-ground level means that less local-regional pol-lution is required to exceed air quality stand-ards. In addition, the increased background has resulted in ozone being rated the third most significant greenhouse gas after carbon dioxide and methane by the IPCC.

Particles – a problem with many facesAtmospheric particles have received increasing attention, both because of their role as air pol-lutants, and as an atmospheric aerosol that af-fects the radiation balance of the atmosphere. There are nevertheless great uncertainties with respect to how the particles, and the diverse set of phenomena they represent, should be con-sidered in relation to both health effects and climate change.

over The laST ten years the main focus in co-ordinated air pollution policies in Europe and North America has shifted from controlling emissions of pollutants causing effects on eco-systems to particles and their role as a human health hazard. The background to this is in-

creasing evidence that fine particles are likely to cause the premature deaths of hundreds of thousands of people annually in Europe and North America. This evidence has been the main driver of the development of new air quality legislation. However, there are great uncertainties in the assessment of what parti-cles and which properties of the particles cause the effects. Present abatement strategies are therefore directed towards all small, inhalable particles, regardless of origin.

parTicleS alSo play an increasing, not yet fully understood role in the climate system. It is ob-vious that different types of particles can in-fluence climate, either as magnifiers or as sup-pressors of the global warming effect. “White” particles with high capacity to reflect sunlight mainly act as a cooling agent, while soot and other “black” particles have a great capacity to absorb sunlight. In addition, particles are significant in the formation and duration of clouds, as well as their ability to reflect sun-light. The complexity of the optical properties, and the uneven distribution of particles in the atmosphere, makes estimates of the role of par-ticles in the climate system highly uncertain.

Climate change – on the threshold of large-scale actionFor a long period in the establishment of far-reaching control of atmospheric pollutants, no or little attention was paid to greenhouse gases and climate change. Emissions of green-house gases (GHGs) continued to increase. Few attempts were made to control GHGs until the 1990s. Some of the earlier air pollu-tion policies have been of great significance for climate change. This is especially the case for the control of ozone-depleting substances such as CFCs (chloroflourocarbons, known as ‘fre-ons’), which not only deplete the stratospheric ozone layer, but are also very powerful green-house gases. The detection of the widespread destruction of stratospheric ozone over Ant-arctica prompted the control of ozone-deplet-

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8 AIR POLLUTION ANd CLIMATE CHANGE

ing substances (ODS) under the Montreal Pro-tocol. Climate change policies over the past 20 years have benefited considerably from the control of ODS. Ozone-depleting substances and other halocarbons, such as HFCs and PFCs partly used to replace them, are never-theless very significant greenhouse gases.

air polluTion and energy policies, as well as economic drivers, have resulted in a decrease in use of fossil fuels in many countries, with a consequential reduction in carbon dioxide emissions. After the oil crises in the 1970s, several countries changed their energy policies in the direction of lower dependence on fos-sil fuels. Changes towards renewable sources such as bioenergy and wind power, measures to save on energy use and the introduction of

nuclear energy in some countries can also be viewed as measures to mitigate climate change. These actions have not been sufficient to af-fect the overall increase in global emissions of greenhouse gases.

a major STep forward in controlling green-house gases was taken in 1992, when the Unit-ed Nations Framework Convention on Cli-mate Change (UNFCCC) was signed. Under the Kyoto Protocol, signed in 1997, a first step was taken towards establishing binding targets for emission reductions for the main long-lived greenhouse gases including carbon dioxide, methane and nitrous oxide. They are also the focus for the negotiations on a new protocol expected to be signed in Copenhagen this year (2009). These negotiations do not include the

Figure 1.3 In the past air pollution abatement strategies were focused on emissions from factories and large combustion plants (left). Although the notion that these emission sources are the dominant cause of emissions of air pollutants, including greenhouse gases, is still prevalent in the minds of many people, in reality lifestyle-dependent activities such as transportation (right), food and other consumption are critical drivers of environmental impact today.

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short-lived atmospheric components that have strong potential to affect the climate, such as ozone and black carbon.

aS iS evidenT from Figure 1.4, the development of carbon dioxide and sulphur dioxide emis-sions has been very different. While sulphur emissions can be reduced by cleaning technol-ogies, choice of fuels and other measures that do not interfere greatly and directly with west-ern lifestyles, emissions of carbon dioxide are closely linked to modern industrialised society. Action to substantially reduce carbon dioxide emissions is therefore harder to take without lifestyle changes.

Common sources but different driversIn Europe, North America and other highly in-dustrialised parts of the world, climate policies today are considered to be far more important

than air pollution policies. Air pollution has be-come a second-order problem. This is not the case in all parts of the world. In many coun-tries, in particular in megacities in fast-growing economies, the air pollution situation has be-come extremely serious. In these cities, protec-tion of human health is becoming a more urgent issue than the more vaguely expressed forecasts of a changing climate. Developing global poli-cies for climate change may therefore be viewed differently depending on a person’s perspective.

many of The sources of air pollutants and greenhouse gases are the same. The need for a combined strategy meeting the challenges of both climate change and air pollution has thus become more and more evident. There is also increasing evidence that abatement costs in re-lation to the total benefits can be reduced sig-nificantly if climate change and air pollution control strategies are developed jointly. Today,

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0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

50,000

1990 1992 1994 1996 1998 2000 2002 2004 2006Year

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

4,000,000

4,500,000

5,000,000

SO2

SO2, kton

CO2

CO2, kton

the whole cost of abatement is visible but only one benefit, for climate or for air pollution, is apparent at a time.

Nitrogen – the root of many problemsAtmospheric emissions of reactive nitrogen compounds, primarily nitrogen oxides and ammonia, contribute to several environmental problems, from local problems of high nitro-gen dioxide concentrations, regional prob-lems such as eutrophication of terrestrial and aquatic ecosystems, acidification of soils and surface waters and ground-level ozone, to the global effects on climate of nitrous oxide. The complexity of nitrogen pollution is illustrated in Figure 1.5. This diversity of effects is mostly not seen in combination. Different effects are often considered in isolation. This most prob-ably leads to suboptimal mitigation strategies, and to a perspective on the true benefits of emission control which is too limited.

The moST SignificanT forms of reactive nitro-gen are ammonium (NH4

+) and nitrate (NO3-).

The dominant source of ammonium is agricul-ture, where fertilisation results in emission of ammonia, which is converted to ammonium (NH3), later deposited in ecosystems. Nitrate is formed from nitrogen oxides (NOx), which

are formed in combustions processes in vehicle engines, power plants and industry, where the nitrogen and oxygen of the air reach tempera-tures that cause them to react with each other.

Climate change interacts with air pollutionClimate change induced by greenhouse gases not only influences the behaviour of the at-mosphere and weather systems over land and sea. It also brings with it modifications of a range of physical, chemical and biological processes within the terrestrial and marine ecosystems. Many of these process changes di-rectly or indirectly affect the composition of the atmosphere, with respect to both atmos-pheric pollutants and greenhouse gases. Our understanding of these processes is still in its infancy and there is a great need for research to understand and assess these processes in re-lation to control strategies and expected future environmental effects.

firST, climaTe change will change vertical and horizontal transport in the atmosphere, leading to changes in the way pollutants are dispersed and transported. Following that, the residence time of air pollutants in the atmosphere may change. In this respect changes in amount and

Figure 1.4 Emissions of carbon dioxide (CO2) and sulphur dioxide (SO2) in EU27 between 1990 and 2006. The divergence of the trends for the two pollutants is striking. It reflects the fact that society has been much more successful in reducing sulphur emissions than carbon dioxide. Data from EEA.

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transportdispersion

conversion

transportdispersion

conversion

agriculture combustion

dry andwet

deposisionto

ecosystememissions of

nitrogen oxides NOx

atmosphericnitrate NO3

-atmospheric

ammonium NH4+

atmosphericgaseous NH3

emissions ofammonia NH3

atmosphericNOx = NO + NO2

climaTe change may also influence the ef-fects of atmospheric pollutants, in particular ecosystem effects. The vulnerability of ecosys-tems may change. For example, an altered cli-mate may change the rate of gas exchange of plants, strongly influencing the uptake of pol-

lutants. A warmer climate is likely to increase the decomposition of organic matter, which is of great significance to ecosystem function. Furthermore, air pollution, such as by ground-level ozone with its adverse effects on plant growth, may lead to less carbon being accu-mulated in the world’s ecosystems, thus pro-moting the accumulation of carbon dioxide in the atmosphere.

emiSSionS of reacTive nitrogen sooner or later end up in ecosystems. There they can be partly converted into nitrous oxide, which is a very potent greenhouse gas. This is another exam-ple of ways in which air pollution can enhance climate change.

climaTe change may cause feedback in terms of changes in emissions and emission patterns. These may be caused by effects on natural sources, e.g. changes in emissions of wind-

Figure 1.5 Nitrogen gas is the main component (78%) of the atmosphere. This form of nitrogen cannot be used directly by most organisms, which is one reason for nitrogen being the limiting nutrient in most ecosystems. Human activity has led to large-scale conversion of nitrogen gas to what are known as reactive nitrogen forms, those that can be used as nutrients by plants and other organisms.

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The vulnerability of ecosystems may change. For example, an altered climate may change the rate of gas exchange of plants, strongly influencing the uptake of pollutants

pattern of precipitation are of particular im-portance to the distribution of air pollutants, but an increase in intensity and duration of stagnant weather situations may also substan-tially affect the levels of urban pollution.

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blown dust, increased emissions of biogenic VOCs such as isoprene and terpenes from forests, which are greatly dependent on tem-perature. Changes in climate may also affect the frequency and intensity of forest fires. Such events may influence not just air pollution but also climate change.

anThropogenic emiSSionS may also be influ-enced by climate change. Energy consumption and thus emissions from combustion may al-ter due to climate change. In large parts of the world, electric power consumption is expected to increase with warmer summers and a great-er need for air conditioning

About this book As explained in this introduction, air pollu-tion and climate are inseparable. Sources, at-mospheric behaviour and effects on man and ecosystems cannot be considered separately, in particular since we are entering an era of increasing concern over both problems. In the various chapters of this book, a number of dif-ferent aspects of the interaction between cli-mate change and air pollution will be further elaborated in order to aid understanding of these links and to make visible the prospects and benefits of co-control of air pollution and climate change.

Figure 1.6 Ecosystems are influenced by air pollutants and climate change on very large scales. Localised strong air pollution effects around large point sources still occur, in particular in developing countries, but the major part of the impact today takes place on broader geographical scales. Reactive nitrogen is dispersed over large areas, leading to a multitude of effects on terrestrial and aquatic ecosystems (left), while climate change has the potential to profoundly alter the natural environment, mountain ecosystems (right) being among the most vulnerable. In the future forests may cover what today is an alpine landscape. Effects of nitrogen and climate change are likely to interact strongly: both affect species composition, and the circulation of nutrients such as nitrogen is highly sensitive to climatic conditions.

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14 AIR POLLUTION ANd CLIMATE CHANGE

IsBN 978-91-620-1278-6

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Air pollution and climate change are often treated as if they were two separate problems, when they actually represent the same scourge. While the former has the most acute impact on human health, and causes economic harm to buildings, vegetation and activities such as tourism, the latter affects lives, property and the natural world in a less direct way, th-rough weather disasters, windstorms, floods, droughts and rising sea levels.

But emission sources for air pollutants and greenhouse gases coincide, and there is great benefit in simultaneously cutting emissions of air pollutants and greenhouse gases. A combined strategy reduces the cost of counteracting both these threats to human health and wellbeing of society.

The aim of this book is to highlight the important links between climate change and air pollution. It will stimulate discussion among scientists, policy makers, environmentalists and others involved in these matters. The authors have a wide range of expertise, from policy making to atmospheric science, environmental medicine and ecotoxicology.

Two sides of the same coin?