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& CLIMATE CHANGE Air Pollution and Climate Change AIR POLLUTION Two sides of the same coin? Two sides of the same coin? Chapter 1 Common Roots of Air Pollution and Climate Change 2 Air Pollution and Climate Change Contents FROM THE BOOK 1 Common Roots of Air Pollution and Climate Change 2 Development of Greenhouse Gas and Air Pollution Emissions 3 Atmospheric Aerosols – Cooling and Warming of the Climate 4 Ozone and Methane – Climate and Environment Connected 5 Nitrogen Effects on Ecosystems in a Climate Change Perspective 6 7 Climate Change Modifies Air Quality 8 Air Pollutants and Greenhouse Gases – Options and Benefits from Co-Control 9 Air Pollution and Climate Change – the Case for Integrated Policy from an Asian Perspective 10 Air Pollution and Climate Change Links – a United States Perspective 11 Towards a Joint Strategy for Air Pollutionand Climate Change Air Pollution Interacts with Climate Change – Consequences for Human Health Chapter 1 Peringe Grennfelt Common Roots of Air Pollution and Climate Change The atmosphere is one of the largest waste disposal units for modern society. For thousands of years it has handled gaseous and particulate waste from combustion and other human activities. It has also been found to have great self-cleaning capacity. Most air pollutants disappear from the atmosphere within a few days after being emitted through deposition to the ground, in particular through washout by precipitation. Some of the less water-soluble compounds, such as many volatile organic compounds (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 compounds. They will remain in the air far longer. They are of particular interest if, like carbon dioxide and nitrous oxide, they affect the radiation 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. Indirectly they are clearly pollutants, as they occur in concentrations that adversely affect ecosystems, 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 included 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 contribution both to toxic effects and to climate change. 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 residence time and physical and chemical properties of a number of important air pollutants and greenhouse gases and particles are of particular importance in environmental risk assessment. The main compounds of significance 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 emissions have declined substantially in Europe and North America due to national and coordinated international action. This has been particularly the case for sulphur. Substantial emission reductions for particles, nitrogen oxides and volatile organic compounds have also been achieved (Table 2). 3 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. Chapter 1 The forces driving European emission reduc- tions have included both health and ecosystem 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 December 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 reaches the ground is increased. In North America, the primary force driving air pollution control was the occurrence of photochemical smog, with the greatest problems occurring on the American west coast, in particular in the Los Angeles Basin. The emission reductions to control photochemical smog were directed towards nitrogen oxides 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 coordination. In the late 1960s, several observations altered the perception of air pollution as a local phenomenon. 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 country could contribute to adverse effects in other countries. There were also several observations of severe ecosystem damage, in particular acidification of surface waters, due to long-range transported air pollution. The transboundary transport of these pollutants made it clear that there was a need for coordinated international efforts to control emissions. These insights 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 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, affectsphotosynthesis 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 5 6 Air Pollution and Climate Change Ground-level ozone 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. – 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 recognised 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 attributed to large emissions of nitrogen oxides and volatile organic compounds under conditions that strongly promoted photochemical ozone production: abundant solar radiation and limited 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. more than 90% from peak levels. As shown in Table 1.2, within the European Union (EU27), sulphur emissions were reduced by 70% between 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. 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 4,320 4,135 -4 5,120 4,094 -20 Ammonia, NH3 Tg SO2 60 50 40 30 20 10 0 2004 2000 1995 1990 1985 1980 1975 1970 1965 1960 1955 1950 1945 1940 1935 1930 1925 1920 1915 1910 1905 1900 1895 1890 1885 1880 Figure 1.2 Emissions of sulphur dioxide in Europe over the period 1880-2005. Source: Vestreng et al, Atmospheric Chemistry and Physics 2007. Chapter 1 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 observed at the same time over large areas of both Europe and North America in connection 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 realised that superimposed on these continental episodes there was a continuously rising background concentration of ozone over the entire Northern Hemisphere. Air pollution and climate change issues con- verge in the increasing background concentrations of ozone. Despite mostly not exceeding any air quality standards, the rising background level of ozone will probably lead to reduced plant growth as well as adverse effects on human health. In addition, a higher background level means that less local-regional pollution is required to exceed air quality standards. 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. 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 particles 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 obvious that different types of particles can influence climate, either as magnifiers or as suppressors 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 sunlight. The complexity of the optical properties, and the uneven distribution of particles in the atmosphere, makes estimates of the role of particles in the climate system highly uncertain. Climate change – on the threshold Particles – a problem with many faces of large-scale action Atmospheric particles have received increasing attention, both because of their role as air pollutants, and as an atmospheric aerosol that affects 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 considered in relation to both health effects and climate change. For a long period in the establishment of farreaching control of atmospheric pollutants, no or little attention was paid to greenhouse gases and climate change. Emissions of greenhouse gases (GHGs) continued to increase. Few attempts were made to control GHGs until the 1990s. Some of the earlier air pollution 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 ‘freons’), which not only deplete the stratospheric ozone layer, but are also very powerful greenhouse gases. The detection of the widespread destruction of stratospheric ozone over Antarctica prompted the control of ozone-deplet- 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 ecosystems to particles and their role as a human health hazard. The background to this is in- 7 8 Air Pollution and Climate Change 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. ing substances (ODS) under the Montreal Protocol. 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 nevertheless 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 fossil 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 affect the overall increase in global emissions of greenhouse gases. A major step forward in controlling green- house gases was taken in 1992, when the United Nations Framework Convention on Climate 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 9 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 emissions has been very different. While sulphur emissions can be reduced by cleaning technologies, choice of fuels and other measures that do not interfere greatly and directly with western 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 drivers In Europe, North America and other highly industrialised parts of the world, climate policies today are considered to be far more important than air pollution policies. Air pollution has become a second-order problem. This is not the case in all parts of the world. In many countries, in particular in megacities in fast-growing economies, the air pollution situation has become extremely serious. In these cities, protection of human health is becoming a more urgent issue than the more vaguely expressed forecasts of a changing climate. Developing global policies 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 relation to the total benefits can be reduced significantly if climate change and air pollution control strategies are developed jointly. Today, 10 Air Pollution and Climate Change 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 problems Atmospheric emissions of reactive nitrogen compounds, primarily nitrogen oxides and ammonia, contribute to several environmental problems, from local problems of high nitrogen dioxide concentrations, regional problems 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 probably leads to suboptimal mitigation strategies, and to a perspective on the true benefits of emission control which is too limited. are formed in combustions processes in vehicle engines, power plants and industry, where the nitrogen and oxygen of the air reach temperatures that cause them to react with each other. Climate change interacts with air pollution Climate change induced by greenhouse gases not only influences the behaviour of the atmosphere 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 directly or indirectly affect the composition of the atmosphere, with respect to both atmospheric 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 relation to control strategies and expected future environmental effects. The most significant forms of reactive nitro- gen are ammonium (NH4+) and nitrate (NO3-). The dominant source of ammonium is agriculture, 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 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 CO2, kton SO2, kton 50,000 5,000,000 45,000 4,500,000 40,000 4,000,000 35,000 3,500,000 30,000 3,000,000 25,000 2,500,000 20,000 2,000,000 1,500,000 15,000 CO2 10,000 0 1,000,000 SO2 5,000 1990 1992 500,000 1994 1996 1998 Year 2000 2002 2004 2006 0 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. Chapter 1 pattern of precipitation are of particular importance to the distribution of air pollutants, but an increase in intensity and duration of stagnant weather situations may also substantially affect the levels of urban pollution. 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 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 groundlevel ozone with its adverse effects on plant growth, may lead to less carbon being accumulated in the world’s ecosystems, thus promoting the accumulation of carbon dioxide in the atmosphere. Emissions of reactive nitrogen sooner or later Climate change may also influence the ef- end up in ecosystems. There they can be partly converted into nitrous oxide, which is a very potent greenhouse gas. This is another example of ways in which air pollution can enhance climate change. fects of atmospheric pollutants, in particular ecosystem effects. 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 pol- 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- atmospheric ammonium NH4+ transport dispersion conversion atmospheric gaseous NH3 emissions of ammonia NH3 agriculture atmospheric nitrate NO3- transport dispersion conversion dry and wet deposision to ecosystem atmospheric NOx = NO + NO2 emissions of nitrogen oxides NOx combustion 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. 11 12 Air Pollution and Climate Change blown dust, increased emissions of biogenic VOCs such as isoprene and terpenes from forests, which are greatly dependent on temperature. 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 influenced by climate change. Energy consumption and thus emissions from combustion may alter due to climate change. In large parts of the world, electric power consumption is expected to increase with warmer summers and a greater need for air conditioning About this book As explained in this introduction, air pollution and climate are inseparable. Sources, atmospheric 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 different aspects of the interaction between climate 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. 13 14 Air Pollution and Climate Change Two sides of the same coin? 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, through 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. ISBN 978-91-620-1278-6 ,!7IJ1G2-abchig!