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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
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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-
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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.
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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.
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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
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