Download MASTER THESIS`S 2010

Combined Effects of Tropospheric
Ozone and Climate Change on
Global Vegetation
Faridullah Nazar Muhammad
Degree project for Master of Science
in Atmospheric Science
45 hec
Department of Plant and Environmental Sciences
University of Gothenburg Sweden
MASTER THESIS 2011
Combined Effects of Tropospheric Ozone
and Climate Change on Global
Vegetation
Faridullah Nazar Muhammad
Department of Plant and Environmental Sciences
Master thesis in Atmospheric Science
University of Gothenburg
Göteborg – Sweden 2011
ii
MASTER THESIS 2011
Combined Effects of Tropospheric Ozone
and Climate Change on Global
Vegetation
Master thesis in Atmospheric Science
Faridullah Nazar Muhammad
Department of Plant and Environmental Sciences
University of Gothenburg
Box 461, 405 30 Göteborg
Sweden
Telephone +46 (0)31-786 0000
Supervised by:
Dr. Göran Wallin and Professor Håkan Pleijel
Department of Plant and
Environmental Sciences
University of Gothenburg
Sweden
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ACKNOWLEDGMENT
Thanks to God
I’d like to convey special thanks and appreciation to my parents
and brothers for their care and encouragement during my study.
Many persons have contributed to the success of this project in my
award of a Master’s Degree in Atmospheric Science. Firstly, I’d like to
express my deepest thanks to my supervisor Dr. Göran Wallin who
supervised me throughout the project. His patience and guidance kept me
on the proper track of my research. Thanks also to Professor Håkan
Pleijel for always being helpful throughout my work and being warm,
welcoming, and supportive and helping me with structure of my work.
The most and above all, I missed my great parents while living far
from them and I am also thankful to Dr. Masood Hamid and my brother
Muhammad Humayun Khan, and two other special persons Farid Asad
Hamid and Muhammad Arif Saeed for all their love and encouragement
to complete my studies. I don’t forget to thank all our friends who helped
me morally to continue and finish this thesis work.
23 May, 2011
Faridullah Nazar Muhammad
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Contents
Abstract .......................................................................................................................... 1
1. Introduction ................................................................................................................ 2
1.1 Ozone is toxic to plants ........................................................................................ 2
1.2 Overview of environmental effects of ozone ....................................................... 2
Troposheric ozone is the ............................................................................................ 2
1.2.1 Ozone effects on vegetation .............................................................................. 2
1.2.2 Ozone effects on human health ......................................................................... 3
1.2.3 Ozone effects on other things ........................................................................... 3
1.3 Example of the toxic features observed on different plants species .................... 4
1.4 The history of ozone measurements and affects .................................................. 4
1.5 What is the cause for the production of ozone in the atmosphere? The main
sources and mechanisms ............................................................................................ 5
1.6 Formation of ozone .............................................................................................. 5
1.7 How ozone is taken up by the plants and why is it toxic ..................................... 7
1.8 Interaction of increases in tropospheric ozone concentrations and climate
changes ....................................................................................................................... 7
1.9 Ozone transport and deposition ........................................................................... 8
1.10 Influence of climate on ozone exposure ............................................................ 9
1.11 Ozone is greenhouse gas .................................................................................. 10
2. Aim and purpose of the study .................................................................................. 11
3. Methods and approach ............................................................................................. 11
3.1 Conceptual model/system description ............................................................... 11
3.2 Ozone and climate interaction ........................................................................... 12
3.3 Ozone effect mechanism to plant ....................................................................... 12
3.4 Ozone, plant and climate change mechanistic processes ................................... 13
3.5 Methods.................................................................................................................. 14
4. Results and discussion ............................................................................................. 15
4.1 Which are globally the main hot spots for ozone effects at present and in the
future on vegetation?................................................................................................ 15
4.2 What kinds of climate change are likely to occur in these regions? .................. 23
4.3 Which kind of interaction between ozone versus climate change and elevated
CO 2 are likely in these regions? .............................................................................. 25
4.4 How will these interactions affect the productivity and carbon sequestration of
plants in these regions? ............................................................................................ 26
Conclusions: ................................................................................................................. 27
References .................................................................................................................... 28
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Combined Effects of Tropospheric Ozone and Climate Change
on Global Vegetation.
Faridullah Nazar Muhammad
Abstract
From recent studies it has been found that tropospheric ozone (O 3 ) is a major problem
around the world, which affects vegetation and human health and also plays an important
role in climate change. Ozone affects yield and quality of many agricultural and
horticultural crops. Also, the O 3 toxicity to plants is likely to reduce carbon sinks in
ecosystems. In the future, the O 3 levels will depend on the anthropogenic emission, the
development of temperature, humidity and solar radiation. There is an increase in mean
O 3 concentrations over large parts of the world. Emissions from combustion of fossil fuel
and biomass are expected to result in approximately a doubling of the global mean
tropospheric ozone concentration during the 21st century. Global climate change and
ozone pollution share some of the anthropogenic causes, but have different properties and
differs impacts.
Changing climatic conditions and stomata response to increased levels of CO 2 plays
central role for ozone risk to plants. When ozone is combined with elevated CO 2 , yield
loss is likely to be considerably less than with ozone alone, mainly because of the
predicted decrease in stomatal conductance at elevated CO 2 , which will reduce the ozone
uptake. Ozone may decrease the concentrations of carbohydrates and sometimes increase
concentration of nutrients, whereas elevated CO 2 reduced nutrient concentrations and
increased carbohydrates concentrations. However, the interaction between O 3 and CO 2 is
unclear.
Current and future formation and effects of ozone are likely to increase in areas
where the factors for ozone formation are suitable. Especially the formation and effects
are expected to increases in Africa, Latin America and some parts of Asia such as China
and India. For future emissions reductions and air pollution control, it is essential to
follow the legislation, agreements and climate change policies, which will decrease the
concentration of tropospheric ozone and other pollutants. There result will be less effects
on the global vegetation and human health. Recent scientific publication predicts that
some parts of the world still will have increasing concentrations of tropospheric ozone.
The increasing concentration of tropospheric ozone in these areas will probably affect the
global vegetation and climate. Important actions for the future is to identify areas with
large future potential effects in which the ozone formation is large, the climate, weather
conditions and water availability promote ozone uptake and where sensitive trees and
crops are grown. The use of O 3 resistant trees and crops may be necessary in these areas.
1
1. Introduction
1.1 Ozone is toxic to plants
Recent studies show that ozone is a big problem around the world which affects
vegetation and humans and contribute also to climate change (Emberson et al., 2003).
Ozone causes different types of damage to crops and other plants such as leaf injury in
the form of bifacial chlorotic and necrotic lesions on a large number of plant species that
have been reported from heavily polluted parts of the world. Visible injury on trees
related to short-term exposure to high ozone concentrations, has been recorded. Broadleaved trees have exhibited chlorosis, bleaching, flecking, stipling and necrosis while tip
necrosis, mottling and banding were observed in conifers (Emberson et al., 2003).
Growth reduction from chronic exposures as well as crop yield losses, reductions in
annual biomass increments for forest trees and shifts in species composition of seminatural vegetation are other well-documented effects of ground-level ozone (Emberson et
al., 2003). Current levels of ozone reduce yields of major staple crops such as rice (Oryza
sativa), wheat (Triticum aestivum), corn (Zea mays), potato (Solanum tuberosum) and
soybean (Glycine max). Ozone impairs photosynthesis and phloem loading, resulting in a
reduced assimilate partitioning to roots and grains. Carbohydrates are retained in leaves
which contribute to (1) higher shoot/root biomass ratio, (2) lower harvest index and (3)
changed leaf chemistry (Fuhrer, 2009).
1.2 Overview of environmental effects of ozone
Troposheric ozone is the major ingredient in photochemical smog and, as mentioned
earlier, represents a considerable risk to vegetations and human beings. Effects of ozone
may occur at various levels of organization, i.e. from the cellular level through the level
of individual organs and plants to the level of plant communities and ecosystems (WHO
Denmark, 2000).
1.2.1 Ozone effects on vegetation
Some of the most important features ozone effects on vegetation include:
•
•
Once O 3 enter the leaf, it reacts with components of cell walls and plasma
membranes forming active oxygen species and hydrogen peroxide, which can be
toxic for plant cells (Valkama et al., 2007).
The effect on the plasma membrane can cause changes in membrane functions
and changes the osmotic potential of the cytoplasm, which in turn can reduce
photosynthetic processes.
2
•
•
•
•
•
•
•
•
•
Visible injury, present as fine yellow/brown/red specks initially on the upper leaf
surface that gradually coalesce to form large lesions (Emberson et al., 2003).
The combined effects of reduced assimilation and increased respiratory loss of
carbon dioxide consist of an overall reduction of assimilate production and export
from the source leaves.
Ozone causes decreased ability to over-winter or survive natural stresses (e.g.
drought, freezing).
Ozone injuries promotes insect herbivory (Chappelka et al., 1997).
The most important impact of ozone on pl ant communities through shifts in
species composition, loss of biodiversity, and changes in genetic composition.
Damage of agricultural crops, forests, and wilderness areas resulting in economic
loss and social values.
Elevated ozone also affects on the pasture production and forage quality
Ozone has for decades been shown to affect the health and production of
agricultural crops and forests in Europe, Canada and United States, especially in
southern California.
Large increases in yield losses caused by ozone in rice, wheat, maize and soybean
in East Asia 2020.
1.2.2 Ozone effects on human health
Examples of significant effects on ozone on human health are:
•
•
•
•
Ozone attacks cells and breaks down tissue and increased sensitivity to allergens.
Decreased ability to breathe, coughing, and respiratory diseases such as pneumonia
and lung damage.
Risk groups: sensitive healthy adults (5-25%), children, individuals with respiratory
disease, exercising individuals.
According to EPA, about 15,000 A mericans die every year from exposure to airborne pollutants; ozone is a plant toxin, enforced by presence of SO 2 and NO x .
1.2.3 Ozone effects on other things
There are further environmental effects of ozone, for example:
•
•
•
•
•
O 3 contributes to global warming. Ozone is the third most important greenhouse gas.
Rubber, textile dyes, fibers, and certain paints may be weakened or damaged by
exposure to ozone.
Some elastic materials can become brittle and crack, while paints and fabric dyes may
fade more quickly.
It also damages cotton, acetate, nylon, polyester, and other textiles.
Reactions involving ozone also cause deterioration of electronic devices.
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1.3 Example of the toxic features observed on different plants species
Ozone significantly reduced the photosynthetic rate of radish (Raphanus sativus) and
turnip (Brassica rapa) plants by 28% and 15% in Egypt (Emberson et al., 2003). O 3
impacts observed as reductions in photosynthetic rate, stomatal conductance and
chlorophyll content summer vegetable, Jew’s mallow (Lycopersicon esculentum Mill)
(Emberson et al., 2003). O 3 injury has been observed on many herbaceous plants at
Ajusco in Mexico City. O 3 caused foliar injury on Pinus hartezumae and Pinus
montezumae and the O 3 -induced symptoms observed on Pinus hartwegii increased with
higher altitudes (Emberson et al., 2003). In Abies religiosa, the first visible injury
symptoms appears as the formation of small whitish lesions on t he upper surfaces of
older needles and these lesions turn reddish-brown in colour and become necrotic and
shed from tree Ozone also effects black cherry (Prunus serotina), Eucalyptus globulus
and different varieties of bean (Emberson et al., 2003). The result of meta-analysis
demonstrated that, in terms of leaf chemistry, angiosperms are more responsive to
elevated O 3 than gymnosperms (Valkama et al., 2007). The variation between species in
responses to elevated O 3 among angiosperms can be exemplified by nutrient
concentrations being reduced in Betula pendula and Populus tremuloides, but increase in
Betula papyrifera and Betula platphylla (Valkama et al., 2007).
1.4 The history of ozone measurements and affects
Shortly after the discovery of ozone by Schönbein in 1839, m easurements of this
atmospheric gas were initiated in a number of locations around the world, including
Europe, South America and North America (Finlayson Pitts and Pitts, 1999). Ozone
measurements during the late 19th century often, but not always, showed concentrations
around 10 ppb ( Volz and Kley 1988). Today, 30-40 ppb i s a typical tropospheric O 3
concentrations found essentially everywhere in the industrialised or heavily populated
parts of the world today. Global increases in ozone have been documented over more
recent times, although the geographical distribution and temporal changes is complex
(Finlayson Pitts and Pitt, 1999). In the 1940s, a remarkable air pollution phenomenon
began to impact the Los Angeles area. In sharp contrast to “London” smog, the ambient
air contained strongly oxidizing, eye-watering and plant-killing pollutants and occurred
on hot days with bright sunshine. Plant pathologists at the University of California,
Riverside, observed a unique type of damage to agriculture crops in the Los Angeles
basin impacted by this phenomenon and reported it as an entirely new form of air
pollution called Los Angeles smog the main component of which was Ozone (FinlaysonPitts and Pitts, 1999). In the 1940s, a remarkable air pollution phenomenon began to
impact the Los Angeles area. In sharp contrast to “London” smog, the ambient air
contained strongly oxidizing, eye-watering and plant-killing pollutants and occurred on
hot days with bright sunshine. Plant pathologists at the University of California,
Riverside, observed a unique type of damage to agriculture crops in the Los Angeles
basin impacted by this phenomenon and reported it as an entirely new form of air
pollution called Los Angeles smog. Ozone was discovered as the component (FinlaysonPitts and Pitts, 1999).Ozone is a highly significant environmental problem presently and
expected to be in the future over large parts of the world.
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1.5 What is the cause for the production of ozone in the atmosphere? The main
sources and mechanisms
Ozone is major and important air pollutant in many parts of the world like North
America, Europe, East Asia, South Asia and central Africa. O 3 is a secondary pollutant,
as it is not directly emitted from sources. Nitrogen oxides (NO x ) and volatile organic
compound (VOCs) are the primary pollutant precursors for O 3 and the combine effect of
increasing methane (CH 4 ) carbon monoxide (CO) has elevated tropospheric O 3 levels
since pre-industrial times (Dentener et al., 2005). The main sources for the emission of
precursor are industries, conurbations, increasing human activities and an increasing
numbers of vehicles. Control measures for NO X and VOCs in North America, Japan and
Europe, have reduced ozone concentration in some areas, but from some parts of Asia,
Latin America, and Africa increases in the ozone concentrations are reported and also
expected in the future. The future the development of ozone concentrations depends very
much on t he anthropogenic emission, temperature, humidity and solar radiation. The
IPCC special reduction scenarios (SRES) indicate that the average ozone concentration
over the northern hemisphere could have increased by 2 to 7 ppb in 2030 and by 20 ppb
in 2100 (Fuhrer, 2009). The largest effects on t ropospheric ozone, from emission
reductions are mainly from air pollutant controls such as precursors for ozone formation.
About one third of the O 3 reductions associated with the Maximum technically Feasible
Reduction (MFR) scenario can be obtained by CH 4 emission controls. MFR explores the
scope for reduced global emissions offered by full applications of today’s most advance
emissions control techniques (Dentener et al., 2005).
1.6 Formation of ozone
The following factors are important for ozone formation:
•
VOCs volatile organic compounds: mostly emitted by motor vehicles, vegetation,
industries, commercial dry cleaners and paints.
•
NO x : emitted from motor vehicles, power plants, industrial facilities, biomass
burning and lightning.
•
High sunlight, temperature and low wind speed play important roles in the formation
of ozone.
•
The highest O 3 concentrations can be found in the summer during dry high pressure
conditions. During inversions (warm air above cooler air) pollutants often get trapped
resulting in high ozone concentrations.
In most of the urban/industrialised areas around the world, formation of ozone is an
essential part of the pollution. Concentrations of ozone are quite variable geographically,
temporally, and altitudinally. The levels of oxidants like O 3 are low in morning and
increases significantly about noon or until dark, depending on emissions and transport
phenomena. The basics of the formation and breakdown of O 3 in the atmosphere are
illustrated in Fig. 1 w hich is based on the following three chemical photodissociation
ofNO 2 in air is critical (Finlayson-Pitts and Pitts, 1999).
NO 2 + hv (λ < 430 nm) → NO + O
(1)
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The free oxygen atom (O) formed can combine with molecular oxygen to form ozone.
O + O2 → O3,
(2)
The reaction of O 3 with NO is driving the breakdown:
O 3 + NO → NO 2 + O 2 ,
(3)
Figure 1. Ozone production from NO x pollutants: Oxygen atoms released from nitrogen dioxide by the
action of sunlight combine with oxygen molecules to form ozone. Nitrogen oxide can combine with ozone
to reform nitrogen dioxide, and the cycle repeats (Figure courtesy NIEHS/NIH).
However, in reality the chemical reactions involved in tropospheric ozone formation are a
series of complex cycles in which carbon monoxide and VOCs are oxidized to water
vapour and carbon dioxide. Oxidation begins with the reaction of VOC or CO with the
hydroxyl radical. Here, the process is exemplified with CO. The hydrogen atom formed
reacts rapidly with oxygen to produce a peroxy radical HO 2 :OH + CO → H + CO 2
(4)
H + O 2 → HO 2
(5)
Peroxy radicals then react with NO to form NO 2 which is photolysed to give atomic
oxygen and through reaction with oxygen a molecule of ozone as described in reactions
(1) and (2):
HO 2 + NO → OH + NO 2
(6)
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The net result of these reactions is.
CO + 2O 2 → CO 2 + O 3
(7)
The periodic intrusion of stratospheric air with its relatively high concentration of O 3
provides an additional source of tropospheric ozone. NO 2 is, however, the major source
of ozone in the troposphere (Finlayson Pitts and Pitts 1999). Ozone is only a problem in
the troposphere where plants, animals and material can be exposed. In the stratosphere
above the troposphere, an ozone layer helps shielding the earth from harmful ultraviolet
radiation. Tropospheric ozone is produced from human activities but to a certain extent
also from emissions from plants and soil, thunderstorms and forest fires.
1.7 How ozone is taken up by the plants and why is it toxic
Ozone is taken up by the plants through stomata, pores on the leaf surfaces that can open
and close. Once O 3 enters the leaf, it r eacts with components of cell walls and plasma
membranes forming reactive oxygen species and hydrogen peroxide, which can be toxic
to plant cells (Valkama et al., 2007). The effect on the plasma membrane can cause
changes in membrane functions and alter the osmotic potential of the cytoplasm, which in
turn can reduce photosynthetic processes in the chloroplasts. Effects of ozone may occur
at various levels of organization, i.e. from the cellular level through the level of
individual organs and plants to the level of plant communities and ecosystems (WHO
Denmark 2000). Elevated O 3 are more response and effected to saplings and mature
trees, but not in seedling. For example, stomatal conductance was shown to be twice
higher in matures trees than in seedling resulting in larger O 3 uptake into leaves
(Valkama et al., 2007).
1.8 Interaction of increases in tropospheric ozone concentrations and climate
changes
There are several potential mechanisms for interactions between ozone, climate change
and the many ways in which the impacts of ozone on ve getation globally may be
modified by changing CO 2 levels. Changing climatic conditions (e.g. temperature and
precipitation) and the stomatal response to increased levels of CO 2 play a central role for
ozone risk to plants. Concentrations of phenolics and terpenes were significantly
increased by 16% and 8%, by elevated ozone and terpene concentrations significantly
increased in response to elevated O 3 in gymnosperms species, in Pinus sylvestris but not
in Picea abies (Valkama et al., 2007). The responses of plants to air pollutants in hot, dry
climates may be influenced by water and temperature stresses. If the stomata are closed,
the uptake of air pollutants decreases and damage to plants is reduced (Emberson et al.,
2003). These authors found that under Special Reduction Emissions Scenario (SRES
A2), ozone concentration by 2100 may increase above 40 ppb i n all regions, and exceed
70 ppb in western and central Eurasia, eastern and western North America, Brazil, central
and south-western African, and East Asia, during the Northern Hemisphere summer.
Future forests will, therefore, face a very different climate than do today’s forests. As a
results of agro-technological developments with introduction of new crops and varieties,
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partly in response to climate change, future agro-ecosystems, and sensitivity to ozone and
other stresses thus making realistic projections difficult (Fuhrer, 2009).
The extent to which ozone exposure increases over this period forms the basis of
predictions of the impacts of the combination of future ozone concentrations and climate
change. Anthropogenic emissions cause the largest driver for ozone formation. Another
major factor influencing future trends in ozone is climate change. The effect of both
factors these factors vary in space and time. Fuhrer (2009) suggested that emissions affect
ozone levels mainly in the mid-latitudes, while climate change effects are strongest in
land areas with strongest warming. IPCC projected warming at mid to higher latitude and
some regions getting wetter and some regions getting driver (IPCC, 2007). In the present
century there is consequently an increasing risk for ozone damage to plants, human health
and climate change (Karlsson et al., 2007). The emissions from combustion of fossil fuel
and biomass have been estimated to double the mean O 3 concentration at the end of the in
21st century (Sitch et al., 2007). The predicted future changes in ozone concentrations,
exposure patterns and global distribution are considered as important component of
global change (Ashmore, 2005).
Increased levels of ozone and carbon dioxide in the atmosphere will in turn affect many
global climatic variables such as temperature, precipitation, UV-B radiation and winds
(Valkama et al., 2007). Ozone effects on vegetation could double the effective radiative
forcing of this gas due to increases in tropospheric ozone, significantly increasing the
importance of changes in atmospheric chemistry as a driver of twenty-first-century
climate change (Sitch et al., 2007). Conversely ozone increases will limit CO 2 fertilization of photosynthesis and reduce the ability of ecosystems to mitigate global
warming (Sitch. et al., 2007). Suppression of the land-carbon sink results in additional
CO 2 emissions accumulating in the atmosphere, therefore indirect radiative forcing of
climate change by O 3 effects on the terrestrial biosphere (Sitch et al., 2007). Methane and
ozone are both key components driving climate change and atmospheric chemistry
(Dentener et al., 2005). Mostly parts of the North Hemisphere photo-oxidation of CH 4
and CO lead to photochemical production of ozone; ozone destruction prevails in NO x
deficient air in parts of tropics and the Southern Hemisphere. The combine effect of
increasing CH 4 , CO, NMVOC, and NOx emissions has elevated tropospheric O 3 levels
since pre-industrial times, associated with a net radiative forcing about 0.35 Wm-2
(Dentener et al., 2005).
Assessments of future ozone risks cannot be made based on i nformation from the
current climate, given the complexity of the interactions between vegetation climate and
ozone. Moreover, effects of climate change, CO 2 and ozone on s oil C overlaps with
strong effects of land use and management (Fuhrer, 2009).
1.9 Ozone transport and deposition
In many parts of the world, ozone formation occurs in one place but affects other place
because of the transport of ozone and the following deposition. The vertical transport
processes and complex interactions that can occur between urban areas, downwind
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regions, and the free troposphere are factors influencing the long range transport.
Emissions from urban regions into the surface layer can be transported into mixed layer
and free troposphere by several mechanisms (Fig. 2), venting up mountain slopes due to
solar heating of the surface, which creates a chimney effect. Clouds also play a role in the
vertical transport (Finlayson-Pitts and Pitts, 1999). Removal of tropospheric ozone from
polluted troposphere by deposition to vegetation may also be an important determinant of
regional air quality.
Ozone deposition comprises several processes; one scale focuses on a tmospheric
processes above the plant canopy, which are governed by wind turbulence and the
roughness of the terrestrial landscape, including altitude and type and density of
vegetation. The second scale, concerns the individual leaf; ozone is deposited to
vegetation canopies through uptake by leaves, mainly through the stomata. The third and
finest scale of resolution is driven by reactions inside the leaf. Phototoxic ozone is
transported from the atmosphere through the stomata and intercellular spaces into the leaf
mesophyll cell. In forests, sinks other than the stomata may also play a role in ozone
deposition, such as cuticles, bark, litter and soil and canopy air space (WHO Denmark
2000).
Figure 2. Ozone pollution can travel from urban to rural areas (Figure courtesy NIEHS/NIH)
1.10 Influence of climate on ozone exposure
When ozone has been taken up b y the leaves, through stomata a production of reactive
oxygen species (ROS) starts. ROS will impairs affect both lipids and proteins which are
essential for all biochemical reactions in the cell. It has been shown to affect the
photosynthetic activity by impairing Rubisco activity, stomatal functioning, and
accelerating leaf senescence (Fuhrer, 2009). Ozone effects are proportional to the
concentration near the leaf surface and the opening of the stomata which is defined by the
leaf conductance to gas diffusion. CO 2 and O 3 enter through the stomata, and both may
influence stomatal conductance and hence flux of the two gases into the leaf. Ozone may
reduce the rate of CO 2 assimilation, and the availability of carbohydrates (Ashmore,
2005).
As the stomata are very responsive to the water status of the plant and vapour pressure in
the air, the responses of plants to air pollutants will be influence by the climate. If the
9
stomata are closed, the uptake of air pollutants decrease and damage to plants is reduced.
Increasing temperatures, altered rainfall and more extreme weather events will change
production potentials with some regions benefiting and others being affected negatively
(Fuhrer, 2009). In the future, ozone levels will depend on t he anthropogenic emission,
curves of temperature, humidity and solar radiation (Fuhrer, 2009). In the present century
increasing risk for ozone damage to plants, human health and climate change (Karlsson et
al., 2007). Increased levels of ozone and carbon dioxide in the atmosphere will in turn
affect many global climatic variables such as temperature, precipitation, UV-B radiation
and winds (Valkama et al., 2007). In northern Sweden future climate change would have
counteracting effects on the stomatal conductance and direct effect of increasing air
temperature and increasing water vapour pressure difference between needles and air
(Karlsson et al., 2007).
Temperature is an important meteorological parameter that affects the formation of ozone
and associated species. Higher temperatures are more conducive to zone formation
because increased thermal decomposition of PAN and HO 2 NO 2 and increased biogenic
emissions are believed to be significant contributors (Finlayson Pitts and Pitts, 1999). In
many developing countries where there is a rapid growth of industries, human activities
and increasing number of vehicles there is also climate conditions that is favouring ozone
formation. The largest increases of O 3 typically occur in the tropics, where high sunlight
conditions prevail, but the rise O 3 affects most of the globe (Prather et al., 2003).
For example, the formation of the primary pollutants precursors for O 3 (NO x and VOC),
are favoured under the climatic conditions of Pakistan with high number of sunshine
hours, higher temperatures, low humidity (Emberson et al., 2003). These conditions are
also likely to be favoured by future climatic changes in many areas. Meteorological
conditions in most parts of India are favourable to O 3 formation which affects crops due
to the long-range transport precursor emissions (Emberson et al., 2003).
1.11 Ozone is greenhouse gas
Ozone is not only affecting plants through toxicity, it can also affect plants by acting as
greenhouse gas (Dentener et al., 2006; Fuhrer, 2009). It is important to note that ozone
has been rated the third most important anthropogenic greenhouse gas after carbon
dioxide and methane (Raes and Hjorth 2005). Climate change policies focus mostly on
CO 2 emissions reductions, although within the Kyoto Protocol, CH 4 and other
greenhouse gases are also considered. Ozone, however, is not part of Kyoto Protocol
(Dentener et al., 2005).
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2. Aim and purpose of the study
•
The aim of this study is to indentify ozone effects on vegetations and in particular the
interactions of ozone effect on vegetation with climate change.
•
An important research question is in which areas these interactions will be most likely
to occur and how ozone risks to vegetation will develop in the future.
•
What is the effect of ozone alone and ozone in combination with elevated CO 2 on
vegetation?
•
In this overview paper it was investigated how hot spots for ozone effects and
different types of vegetation around the world are likely to develop in the present
century considering the effects of climate change and ozone interaction.
3. Methods and approach
3.1 Conceptual model/system description
The combined effects of tropospheric ozone and climate change on global vegetation are
mainly driven by increasing rate of greenhouse gases and changes in temperature,
rainfall, air humidity, radiations, wind and land surface vegetation. Ozone formation and
effects on v egetation depend on t he climatic conditions. If the climate conditions are
suitable for formation of ozone, there may be immediate impacts on vegetation. Climate
change will alter the conditions for chemical reactions in the atmosphere, the atmosphere
transport and how much that is taken up by the vegetation. Assessments of future ozone
risks thus depend on c urrent climate. The interaction between vegetation, ozone and
climate is illustrated in a conceptual model in (Fig. 3).
Figure 3. Chains of interactions between ozone, vegetation and climate change (Fuhrer, 2009).
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This review paper shows that how ozone effects on a nd risks for vegetation could be
affect by and interact with changing climate. The conceptual model shows important
links between (1) ozone production, distribution and ozone exposure, (2) ozone transfer
and plant uptake, (3) vegetation responses to the amount of absorbed ozone, including
detoxification and repair and cellular damage, and (4) climate effects on ozone uptake.
3.2 Ozone and climate interaction
Anthropogenic and natural emissions of gases and greenhouse gases are the reason for
tropospheric ozone formation and in the troposphere. Changes in climate are diverse and
complex impacts on ozone through changes in meteorological conditions affecting ozone
destruction and production. IPCC assumes pronounced warming at mid to higher latitude
and some regions getting wetter and some regions getting drier (IPCC 2007). Climate
change and ozone further interact as they both affect vegetation and land surface
properties (Fuhrer, 2009). The predicted future changes in ozone concentrations,
exposure patterns and global distribution are considered as important components of
global change (Ashmore, 2005). Increased levels of ozone and carbon dioxide in the
atmosphere will in turn affect many global climatic variables such as temperature,
precipitation, UV-B radiation and winds (Valkama et al., 2007).
3.3 Ozone effect mechanism to plant
Ozone effects on pl ants are dependent on l eaf uptake through stomata, leaf surface and
leaf conductance to gas diffusion. Large amounts of ozone damage the functioning of
stomata. Once O 3 enters the leaf, it reacts with components of cell walls and plasma
membranes forming active oxygen species and hydrogen peroxide, which can be toxic for
plant cells (Valkama et al., 2007). The production of reactive oxygen species (ROS)
impairs photosynthetic CO 2 fixation by impairing Rubisco activity and indirectly leaf
senescence and chlorophyll degradation (Fuhrer, 2009). Ozone can inhibit reproduction
by affecting fertilization, germination and abortion of flowers. Ozone impairs phloem
loading and assimilates partitioning to roots and grain is reduced while carbohydrates are
retained in leaves (Fuhrer, 2009). O 3 impacts observed included reductions in
photosynthetic rate, stomatal conductance and chlorophyll content (Emberson et al.,
2003). The first visible injury symptoms as the formation of small whitish lesions on the
upper surfaces of older needles and these lesions turn reddish-brown in colour and
become necrotic and shed from tree (Emberson et al., 2003). Ozone affects vegetation to
a lesser extent in dry area as compared to rainy area because the stomatal conductance is
lower in dryer conditions.
The result of meta-analysis demonstrated that, in terms of leaf chemistry, angiosperms
are more responsive to elevated O 3 than gymnosperms, as shifts in concentrations of
carbohydrates and phenolics were observed in former. Among-species variation in
responses to elevated O 3 with in angiosperm can be exemplified by nutrient
concentrations, which were reduced in Betula pendula and Populus tremuloides, but
increased in Betula papyrifera and Betula platphylla (Valkama et al., 2007). From the
12
hypothesis results of Betula pendula and Populus tremuloides shows that elevated O 3 in
combination with CO 2 exacerbated effects of O 3 in these two species (Valkama et al.,
2007). Ozone in combination with elevated CO 2 significantly increased carbohydrates
concentration by 45% and no s ignificant ozone effect on s ugars but negative effects on
starch. Sapling and mature trees are more responsive than seedling (Valkama et al.,
2007). Concentrations of phenolics and terpenes were significantly increased by 16% and
8%, in response to elevated ozone. However, tannins did not significantly differ from
ambient control. Terpene concentrations significantly increased in response to elevated
O 3 in gymnosperms species, in Pinus sylvestris but not in Picea abies (Valkama et al.,
2007). O 3 impacts on primary metabolites were apparent by tree type, ontogenetic stage
and species. Carbohydrate concentrations decreased in angiosperm trees and in saplings,
while nutrient decrease was observed in some species, like Betula pendula and Populus
tremuloides, and increased in birch species (Valkama et al., 2007).
3.4 Ozone, plant and climate change mechanistic processes
Increased ozone levels can lead to stomatal closure, which in turn limits the damaging
effect of ozone and effects of carbon dioxide fertilization of photosynthesis, carbon
sequestration and reduce the ability of ecosystems to mitigate global warming (Fig. 4).
One possible mechanistic relationship between O 3 and CO 2 is:
O 3 ↑ → Photosynthesis↓ → C sequestration↓ →CO 2 ↑ →Stomatal conductance↓ →O 3
uptake↓ → Climate change or Global warming.
C sequestration
O3
Precursor
Emission
CO2
O3 uptake
Plant growth
Climate Change
Figure 4. Ozone, CO 2 and climate change effects on important plant ecophysiological processes.
When stomata are affected seriously by tropospheric O 3 concentrations than further
uptake of O 3 deceasing by stomata than increased the amount of ozone in atmosphere.
Both CO 2 and O 3 are greenhouse gases, which play important roles in the future climate
change. Climate change may influence all other boxes in Figure 4.
Future O 3 effects on plants are defined by the interplay between ambient O 3 , CO 2 and
climate change on s tomatal conductance and plant production. CO 2 -induced stomatal
closure will protect plants from damaging impact of O 3 . Decreasing soil moisture
13
expected in subtropics, Mediterranean region and increases in East Africa, central Asia
and some other areas has the potential to limit ozone uptake by vegetation, while in areas
with expected precipitation increases with climate change, including high latitudes and
some wet tropics ozone uptake by vegetation may be enhanced (Fuhrer, 2009). Emissions
of ozone precursors affect ozone risk to vegetation mainly in mid- latitudes, while climate
change effects are strongest in areas with the strongest warming (Fuhrer, 2009).
3.5 Methods
In this review paper the combined effects of tropospheric ozone on v egetation and
climate change interaction is assessed. For the review of this paper I searched and
collected information from scientific papers, related books on tropospheric ozone and its
effects on vegetation, climate change and IPCC report 2007. I also made used of relevant
web sites.
The study aims to identify the hot spots for the current levels of ozone and also for future,
which affects different types of vegetation in different parts of the world (Asia, Africa,
North America and parts of Europe). The paper also examines the combined and single
effects of ozone and carbon dioxide on ve getation. Increased ozone levels affects
photosynthesis, carbon sequestration and reduce the ability of ecosystems to mitigate
global warming. From the collected data, I constructed scenarios for where severe,
medium and smaller effects of tropospheric ozone are likely to occur in consideration of
climate change. The results were compiled in tables and maps. Current, and in the future
increasing, ozone concentrations have different kinds of interaction with climate change
that are likely to differ between regions. This kind of variation is reflected in the
scenarios built from the literature search.
Increase in tropospheric ozone concentrations, effects on t he stomatal conductance and
their interactions affect the productivity and carbon sequestration of plants. Depending on
climatic conditions the interaction may vary between different regions? Thus, from the
review of currently available relevant papers, scenarios and models that used for ozone
risk assessment also to influence of climate on stomatal conductance and plant gas
exchange was covered by the study.
14
4. Results and discussion
4.1 Which are globally the main hot spots for ozone effects at present and in the
future on vegetation?
Tropospheric ozone is the major components of photochemical smog which is a risk to
vegetation and human beings. Effects of ozone may be expressed at various levels of
organization, i.e. from the cellular level through the level of individual organs and plants
to the level of plants communities and ecosystems (WHO Denmark, 2000). High
concentrations of tropospheric O 3 pollution has been observed in several areas around the
world (Fig. 5, Table 2) and is still increasing in many areas simultaneously with a
growing number of motor vehicles and development of industrial activities. In some parts
of Asia, Latin America, and the Africa the concentration of ozone precursors have been
predicted to increase in the future. In the present century an increasing risk for ozone
effects on plants, human health and climate have been observed (Karlsson et al., 2007).
There are many types of crops and trees that can be affected by high ozone
concentrations today. There is also long term-term ecosystems effects of ozone where
ozone have cumulative effect on c lover biomass, grassland species and forest
communities in an early stage of succession (Ashmore, 2005). Ozone effects on c rops
varies with their sensitivity to ozone which varies with genotype and yield. C rops and
fruits are affected by ozone in many areas of the world (see Fig 5) e.g. wheat,
watermelon, pulses, cotton, turnip, tomato, onion, soybean and lettuce. Crops can be
classified into: 1) ozone-sensitive e.g. onion, soybean, lettuce, sugar beet, potato, oilseed
rape, rice, maize grape and broccoli; 2) moderately ozone- sensitive e.g. barely and 3)
ozone-tolerant e.g. plum and strawberry (Fuhrer, 2009).
North America: Average tropospheric ozone concentrations in United Stated and
Southern Ontario Canada are 65 nL L-1, which affects vegetation, e.g. edible dry bean,
tobacco, rye and clover. The dominant species of mixed-coniferous forests like
Ponderosa pine and Jeffery pine in the San Bernadino Mountains are the most sensitive
tree species to ozone (Table 2.1). Both species have shown severe foliar injury and
reduce needle longevity (Ashmore, 2005). Ozone causes large yield reductions and
economical impacts on crops over wide geographic areas in both the United States and
southern Ontario in Canada (Table 2.1). Over the period 1990-2100, global Gross
Primary Production (GPP) is projected to decrease by 14-23% owing to plant ozone
damage and with regional reduction above 30%. Large reductions in GPP and landcarbon storage are projected over North America, Europe, China and India (Sitch et al.,
2007). High ozone concentrations are also measured in Mexico (50-65 nL L-1) which
affects several coniferous tree species, e.g. Pinus hartwegii and Abies relgiosa (de Bauer,
2003).
Asia: The air pollution situation in China is dominated by high SO 2 concentrations while
less attention has been paid to NO x and O 3 . However, the relatively limited
measurements of O 3 have shown that high concentrations ozone occurs and it has been
forecasted
to
15
Table 2.1. Hot spots of ozone effects on vegetation and the likely climate change in different parts of North America.
Hot spot
United States
and Southern
Ontario, Canada.
Vegetations
Edible dry bean,
tobacco, rye and red
clover.
San Bernadino
Mountains. Latin
American.
Pinus hartwegii,
Montezuma & Abies
religiosa and Jeffery
pine.
Observed ozone effects
Yield & economically
impact on crops, 3000
billion US$ annual loss in
US, 65 nL L-1.
Severe foliar injury &
reduce carbon allocation,
germination, fertilization.
50-60 nL L-1.
Temperature
Warming from 2 °C to 3°C
western, Southern & eastern
& 5°C in northern in winter
and in Canada 3- 10°C.
Warming largest in south
west USA in summer. Temp:
warming varies from 2°C to
3°C along the WS.
Precipitation
Increase rain on continent
except SW part. Increase
annual mean in north 20% &
30% in winter.
Annual mean precipitation is
very like to decrease in the
southwest USA.
References
Ashmore (2005); Percy
(2003); Wahid et al. (2001).
Ashmore (2005); Person
(2003); (Solomon et al
(2007).
Table 2.2. Hot spots of ozone effects on vegetation and the likely climate change in different parts of Asia
Hot spot
Asia
China
Pakistan
Vegetations
Rice, wheat, corn,
potato and cauliflower,
tomato, wheat, maize,
radish & rice.
Aubergine, cauliflower,
rice Chinese leaves,
tomato, wheat, maize
and radish.
Wheat, rice, mungbean,
chickpea, soybean &
cotton.
Observed ozone effects
Last and reduction in crop
yield. Leaf injury, chlorotic
& necrotic lesions.
Lost 1-9 % yield in wheat,
rice & corn & 23-27 % of
soybeans. In 2020 O 3 65 nL
L-1, in china.
Drastic yield reduction.
(30-50%) in staple crops con:
of O 3 25-45 nL L-1.
Temperature
Mean warming b/w 1999 to
2099 in SE A 2.5 °C, E A 3.3
°C, CA &, Tibet 3.8 °C &
NA 4.3°C.
Median warming is 3.3 °C
by end 21 century.
Median warming is: 3.3 °C.
Indian
Cassia fistula, carissa
carandal & potato
Leaf injury, bifacial chlorotic
&necrotic lesions, 10- 137
nL L-1.
Median warming is 3.3 °C
by end 21st century.
Japan
Japanese fir, Veitch, s
silver fir, Marie, s fir
and birch.
Tree dieback, forest decline
and decline in yield of rice
Median warming: 3.3 °C.
16
Precipitation
Rain largest in North, EA &
CA, western parts. Summer
rain increase in NS, SE &EA,
& decrease in CA.
Increase rain EA & median
change at end of 21st
century20% rain over East
China Sea & decrease N.
Rain decrease in DJF. Median
Change 11% end of 21st
century, -5% in DJF and
11%in JJA.
Increase rain in EA & median
change at end of 21st century,
9%. Rainfall over north areas.
References
Emberson et al. (2003);
Fuhrer (2009).
Wang & Mauzerall (2004);
Solomon et al. (2007).
Emberson et al (2003); Wahid
et al. (2001).
Agrawal (2003); Solomon et
al. (2007).
Izuta (2003).
Table 2.3. Hot spots of ozone effects on vegetation and the likely climate change in different parts of Africa.
Hot spot
South Africa
Vegetations
Crop production
forests of Mpumalanga,
& Fynbos biome.
Observed ozone effects
Caused mild symptoms on
vegetations & visible leaf
injury, 60-90 nL L-1.
South western
African
O 3 conc: by 2100 under
SRES A2 exceed 70 ppb
Visible leaf injury, plant
damage & reduction in crop
yields, 60-90 nL L-1.
Temperature
1999 to 2099, average WA,
SA, EA & Saharan sub,
median temp: increases 3 °C
& 4 °C.
1999 to 2099, the median
temp increases lies b/w 3 °C
&4°C.
Precipitation
20% drying in annual mean
along Mediterranean & SA,
& increases rain in EA.
References
Tienhoven & Scholes (2003);
Sitch et al. (2007).
20% drying in annual mean
along Mediterranean & SA,
and increases rain in EA.
Emberson et al (2003); Sitch.
et al. (2007).
Table 2.4. Hot spots of ozone effects on vegetation and the likely climate change in different parts of Europe.
Hot spot
Europe & Med:
Vegetations
Bean corn, grape, potato,
soybean, tobacco, wheat,
peach & spinach.
Observed ozone effects
Agricultural & horticultural
crops for visible damaged to
commercial fields. nL L-1.
Northern
Sweden
Negative impacts of O 3
on vegetation &
potatoes.
O 3 damage to plant, human
health &forcing climate
change. 30-50 nL L-1.
Temperature
1999 to 2099 varies from 23
°C in NEU & from 2.2°C to
5.1°C in SEM, warming in
NE in winter & Med: area
summer.
Mean air temp: in northern
Sweden during spring and
summer to Increase1 & 2°C
2000 - 2050.
17
Precipitation
Rain increases in north &
decreases SE, increases
northern & CE is in winter &
70% Scandinavian.
References
Ashomre (2003); Sitch et al.
(2007).
The precipitation is increase
10-30% winter & fall, but not
spring & summer.
Karlsson. et al. (2007) ;
Solomon et al. (2007).
Table 2.5. Tropospheric ozone, emissions from fossil fuel and biomass burning effect on future forest and specific five main hot spots in the world that affected
by O 3 .
Hot spots
Future forests.
Vegetations
Phenolics and terpenes, increased 16% & 8%, to
elevated ozone.
Ozone effects
O 3 enter the leaf, it reacts with components of cell
walls & plasma membranes.
References
Valkama et al. (2007).
Forest trees.
O 3 impacts primary metabolites were apparent by
tree type, ontogenetic stage.
Double the global mean tropospheric
ozone & increases in 21 century.
O 3 pollutions is more significant problem in the
future
Valkama et al. (2007)
Emissions from fossil fuel &
biomass burning.
Hot spots (North America,
Europe, North Asia, South Asia
& Central Africa).
Some species e.g. B. pendula & P. tremuloides,
increased & birch species.
Damage plants, reducing plant
primary productivity & crop yield.
Elevated O 3 are still centered on five main hotspots & concentrations
b/w 60 to 70 nL L-1.
In 2020, China,
Japan & South Korea.
Grain loss 2-16% for wheat,
rice & corn & 28-35% for soybean
Economic costs are expected to increase by 82%,
33% & 67%. Average conc of ozone is ≤60 ppb in
2020.
Wang & Mauzerall (2004).
18
Sitch et al. (2007).
Emberson et al. (2003).
increase in a foreseeable future (Zheng and Shimizu, 2003). It has also been shown that several
cultivars of crops common in China are affect by ozone (Table 2.2) (Zheng and Shimizu, 2003).
O 3 is one of the major pollutants in Taiwan and the effects on t obacco leaves and necrotic
lesions observed usually only appeared on leaves of sweet potato and spinach over large area of
Taipei Basin, and cucumber, muskmelon, flowers, vegetables, and guava (Emberson et al.,
2003). In 2020, assuming no change in agriculture production practices, and grain loss due to
increased levels of O 3 pollution is projected to increase to 2-16% for wheat, rice and corn and
28-35% for soybean (Wang & Mauzerall, 2004). Tree dieback and forest decline from the high
concentrations of O 3 in forest areas in Japan. Declines in health of species such as Japanese fir,
Veitch’s silver fir, Marie’s fir, Seybold’s beech and birch can be observed in mountains areas of
Japan and also decline in yield of rice (Izuta, 2003).
The western and northern parts of India are more polluted with a higher risk of adverse air
pollution impacts occurring in the future as compare to other parts of the country. The
meteorological condition in most of the country is favourable to O 3 which affects crops due to
the long-range transport of precursor emissions. Leaf injury in the form of bifacial chlorotic and
necrotic lesions on Cassia fistula and Carissa carandas has been reported from heavily polluted
zones of Varanasi city and recorded evidence of O 3 injury in potato crops in Punjab. Daily mean
O 3 concentrations in Delhi were recorded between 20 and 273 µg m-3 (Wahid, 2003). The levels
of ozone and nitrogen dioxide are increasing rapidly and ozone has today larges impacts on
growth and yield of important crops in Pakistan (Table 3). The plants showed visible symptoms
of O 3 damage under the climatic conditions of Pakistan (Wahid, 2003).
Table 3. Recent experiments studies that have recorded yield losses as result of ozone exposure for several different
crop species in Pakistan (Wahid, 2003).
Crops
Wheat (6 varieties)
Rice (5 varieties)
Soybean (2 varieties)
Chickpea (3varieties)
Mungbean
(2varieties)
O 3 ppb
33-85
35-60
64
59
66
NO 2 ppb
20-30
13-25
29
38
31
Yield losses (%)
29-47 (2000)
28-42 (2000)
37-46
23-27
26-34
Europe: Ozone affects agricultural and horticultural crops in Europe, resulting in e.g. less
economic values. Increasing warming 2.2 °C in Northern Europe and up to 5.1 °C in Southern
Europe are predicted for next 100 years Rain will be increased in Northern Europe and decrease
in Southern Europe (Table 2.4 and 4). In northern Sweden there is increasing risk for negative
impacts of ozone on vegetation, related mainly to ozone concentrations and an earlier onset of
the growing season (Table 2.4) (Karlsson et al., 2007). The northernmost part of Fennoscandia,
i.e. north of the Arctic Circle, the future ozone uptake by vegetation at these high latitudes can
potentially accumulate over a longer growing season. The hypothesis was tested that the ozone
uptake by vegetation in northern Sweden is promoted by a combination of increasing ozone
concentrations and climate change (Karlsson et al., 2007). In the future, the development of
tropospheric ozone depends on the anthropogenic emission, curves of temperature, humidity and
solar radiation (Fuhrer, 2009). Increase in mean ozone worldwide, still in Europe where the
control precursors emissions under United Nations Economic commission for Europe (UNECE)
19
Convention on L ong-range Transboundary Air Pollution (CLRTAP) but more effects of
emissions from Asia, Latin America and Africa (Fuhrer, 2009).
Figure 5. Current annual average ozone concentrations with 75 nL L-1, 60 nL L-1, and 40 nL L-1 around the world.
References and more details are presented in the Table 2.
Africa: In South Africa high O 3 levels may be a natural feature of the region, anthropogenic and
industrial emissions could raise O 3 concentrations that affect crop production. Ozone levels
during the dry season over Africa ranges from 60 t o 90 ppb a s a result of the formation
precursors for tropospheric O 3 formation from the vegetation fires. Ambient O 3 concentrations
represent a risk to the commercial forests of Mpumalanga (South Africa) and potentially
phototoxic events occurred (Emberson et al., 2003). Increasing ozone concentrations caused mild
symptoms on ve getation and visible leaf injury in South Africa and South Western Africa.
Ambient ozone levels reaching concentrations that could have caused mild symptoms on
vegetations, greatest visible leaf injury in winter, affect fynbos biome and xerophytes (less need
of water & less opening of stomata and found in South Africa) plants are resistance to O 3 (Table
2.3) (Emberson et al., 2003). O 3 is the major pollutant in Egypt industrial, urban activities in the
greater Cairo and Alexandria areas. The concentration of ozone has been increasing since the
early 1980s. Exposure to 80 ppb O 3 for eight days, in closed fumigation chambers, significantly
reduced the photosynthetic rate of radish and turnip plants by 28% and 15%. The O 3 impacts
observed included reductions in photosynthetic rate, stomatal conductance and chlorophyll
content (Abdel-Latif, 2003).
20
Figure 6. This map presents likely future hot spot of ozone over the world (USA, Canada, Latin America, Asia,
China, Pakistan, India, Japan, South Korea, S, SW&C Africa, Europe & Mediterranean). References are given in
Table 2.
In Fig 6 likely future hot spots with high troposheric ozone concentrations over the world are
shown with red colour. Increasing attention is being paid to impacts of ozone on crops in regions
characterized by rapid urbanization, industrialization increase in the NO x emissions and by
intercontinental transport of pollutants in China, Japan, South Korea, South Asia, north
hemisphere and Africa, particularly in Zimbabwe (Table 2.2) (Fuhrer, 2009). Ozone
concentrations vary strongly over time with very high episodic peak concentrations in the most
polluted regions during the warmest months and maxima during spring prevailing sites. In
regions like East Asia exposed to summer monsoon, strong seasonal variations in O 3
concentgrations are observed (Fuhrer, 2009). Five main ozone “hot-spots” i.e. North America,
Europe, North Asia, South Asia and Central Africa (Table 2.5) has been identified. Models for
calculating three-month mean O 3 concentrations estimates levels between 60 t o 70 ppb ove r
large part of the regions. Predicted future global O 3 concentrations assume a “business as usual”
scenario. In these predictions, elevated O 3 are still centred on f ive main hot-spots but area
covered by concentrations between 60 to 70 ppb is greatly increased. Global scale measurements
of tropospheric O 3 levels in north hemisphere show normally values between 50 t o 60 ppb
compared with 25 to 30 ppb in the southern hemisphere (Emberson et al., 2003).
Emissions from fossil fuel and biomass burning approximately double the global mean
tropospheric ozone concentration, and increases expected in 21 century (Sitch et al., 2007).
Surface ozone levels greater than 40 ppb , may cause visible leaf injury and plant damage and
reduction in crop yields in USA, EU and East Asia (Table 2.4 & 2.5). Under Special Report on
Emission Scenarios (SRES) A2, and to exceed 70 ppb over western and central Eurasia, eastern
and western North America, Brazil, central and south-western African, and East Asia, during the
Northern Hemisphere summer (Sitch et al., 2007). For the “current legislation” case, both models
(TM3 and STOCHEM) indicate an increase of the annual average ozone levels in the Northern
Hemisphere by 5 ppbv and up t o 15 ppbv ove r the Indian sub-continent, comparing the 2020s
with the 1990 (Dentener et al., 2005). From Intergovernmental Panel on Climate Change (IPCC)
and SRES predicted near-surface ozone to increase by 2030 on average by about 5 ppbv in much
of the NH, compared to the present modelled background levels of 30-50 ppbv. In the “worst
case” (A2p) emission scenario of SRES, ozone may grow by more than 20 ppbv up t o 2100
relative 2000 (Dentener et al., 2005). In analysis suggests for the CLE case a continued increase
of global anthropogenic CH 4 emissions, leading to 35% higher emissions in 2030 than in 2000
21
(Dentener e t al., 2005). The increase in CH 4 from 1750 ppb t o 4300 ppb dr ives half of O 3
increase (Prather et al, 2003).
Ozone is an air quality problem today for much of the world’s population. Even modest
increases in the background abundance of tropospheric ozone might defeat current air quality
standards (AQS) strategies (Prather et al, 2003). The largest increases of O 3 typically occur in
the tropics, where high sunlight conditions prevail, but the rise O 3 affects most of the globe
(Prather et al, 2003). The TM3 model shows that about 520 Tg O 3 yr -1 enters the troposphere
through the 100 hPa and the SOCHI model shows that the resulting ozone flux into the model
domain to 420 Tg O 3 yr -1 The global O 3 burdens from TM3 and STOCHEM show very similar
increases from 450 Tg in 1990 to 470-485 Tg in 2030 in the current legislation (CLU) case, and
decreases to 430 Tg for the Maximum Feasible Reduction (MFR) case (Dentener et al., 2005).
TM3 and STOCHEM showing maximum increases of ozone levels between 8-12 ppbv in India,
Pakistan and Bangladesh, China and South East Asia. Over the North Pacific and Atlantic Ocean
ozone increases by 4-6 ppbv, and increasing ship emissions contributing 1 to 1.5 ppbv. The MFR
scenario explores the scope for reduced global emissions offered by full applications of today’s
most advance emissions control techniques (Dentener et al., 2005). The largest effects on ozone
of emission reductions stems from air pollutant controls, about 1/3 of the O 3 reductions
associated with the MFR scenario can be obtained by CH 4 emission controls (Dentener et al.,
2005).
Figure 7. Major areas with sensitivity of vegetation to ozone concentrations in North America, Western Europe,
Mexico, Pakistan, China, Austria, Belgium, France, Germany, Greece, Switzerland, Netherland, Spain, Sweden and
Italy. References and more information Tables 1, 2 and 3.
In Fig 7, t he vegetation sensitivity to ozone concentrations is shown with yellow colour,
whereas white areas may be not so much sensitivity to ozone or lack of knowledge. Edible dry
bean, tobacco, rye and red clover are affected by ozone in United States, southern Ontario and
Canada (Table 2.1). There have also been several reports that crops are visibly injured by ozone
outside North America and Western Europe (Ashmore, 2005), e.g. on Phaseolus vulgaris in
Mexico (Wahid et al., 2001). Large increases in yield losses caused by ozone in rice, wheat and
maize in East Asia 2020 ( Table1.2) (Wang & Mauzerall, 2004). Lycopersicon esculentum in
New Delhi, and radish and turnip yields at rural site in the Nile delta are other examples. Ozone
22
highly affects yields of winter wheat and other crops. Cereal production at risk was in Asia. In
China estimated increase level of ozone precursors caused significant losses in wheat, soybean,
and maize by 2020 (Ashmore, 2005). Tropospheric ozone affects the crop production, especially
in the forest of Mpumalanga and fynbos biome in South Africa.
Table 4. Crops that have shown ozone injury symptoms in the field, by country in Europe 1990 – 2007 (Hayes et al.,
2007)
Country
Crop
Austria: Bean
Belgium: Bean, Maize, potato,
Snapbean.
France: Bean.
Germany: Bean.
Greece: Bean, chicory, courgette,
maize, Egyptian clover, grapevine,
lettuce, potato, tobacco, watermelon
onion, parsley.
Hungary: Bean.
Country
Crop
Poland: Bean.
Netherlands: Bean, subterranean
clover.
Russian Federation: Bean
Slovenia: Bean
Spain: Bean, clementine, grapevine,
oat, peanut, potato, soybean, tobacco,
tomato, watermelon.
Sweden: Potato, radish, red clover,
subterranean clover, wheat and white
clover.
Switzerland: Grapevine, potato.
Juice quality in grapes was more sensitive to ozone then yield, reduction in both seed yield
and oil content of harvested seeds of oil seed rape in UK and ozone impacts on potatoes at seven
different parts of Europe that effects on crop quality and yield (Ashmore, 2005). Ozone damage
crops by causing visible foliar injuries to 21 crop species in Italy, Spain, and Greece. Crops
damages have also been observed on commercial agricultural and horticultural crops from other
parts of Europe. Ozone affects forest growth and vitality across Europe with visible symptoms of
O 3 injury on bot h young seedling and mature beech trees (Table 2.4 & 4) (Ashmore, 2003).
Mountain birch is an important tree species for northern boreal ecosystems in Sweden that is
affected by increasing concentrations of ozone (Karlsson et al., 2007).
4.2 What kinds of climate change are likely to occur in these regions?
Changing ozone concentrations are important components of global change. Different climatic
conditions may lead to variable impacts of the same concentration of ozone (Ashmore 2005).
Direct effects of ozone may be important to consider in assessing impacts of ozone in the context
of global change. Tree parasitoid interactions could be modified by elevated CO 2 and O 3 in
different ways dependent on g enotype. How these will be altered by rising ozone exposures,
when other elements of global change affects foliar chemistry, emission of volatiles, and insect
population dynamics, is very uncertain (Ashmore 2005). The extent to which exposure to ozone
increases are closely linked to emission scenarios for energy production, transport, agriculture
and industry, which form the basis for predictions of the impacts of climate change, ozone
impacts on food production and ecosystem functions (Ashmore, 2005). Anthropogenic emission
will have strong influences on both ozone and climate change, but the effect of both factors alters
in space. Example from Fuhrer (2009) is that emissions affect ozone levels mainly in the midlatitudes, while climate change effects are strongest in land areas with strongest warming.
23
Figure 8. Areas where climate change is likely to promote ozone damage in East Africa, Central Asia, Subtropics
Mediterranean regions, Mid-latitude, Central and Southern Europe, Pakistan, Northern Sweden and Eastern United
States. References and more information Table 2.
In Fig 8 the red colour shows areas where climate change will promote ozone damage and
white places less effects or where we have lacking knowledge. E.g. in northern Sweden future
climate change would have counteracting effects on the stomatal conductance and needle ozone
uptake, direct effect of increasing air temperature and increasing water vapour pressure
difference between needles and air (Karlsson et al., 2007). Annual mean air temperatures in
northern Sweden will increase between 1 and 2°C during spring and summer from the years
2000 to 2050. The precipitation is predicted to increase 10-30% over the winter and fall, but not
during spring and summer, except for mountain region where it is predicted to increase during
spring (Table 2.4) (Karlsson et al., 2007).
Hot spots of ozone and climate change will have different effects in different parts of America
and Canada. The temperature will increase with 2°C to 3°C in western, southern & eastern USA
and with 5°C in northern part of USA in winter, and an increasing temperature up to 10°C are
predicted for some parts of Canada . Warming will be largest in South West USA in summer.
Increasing rain fall is predicted on the continent except in South West part of USA. The annual
mean rain will increase with 20% - 30% in winter (Solomon et al 2007). In United States and
Canada increasing warming from 2 - 10 °C and increase rain on continent (Table 2.1) (Ashmore,
2005). Tropospheric ozone and climate change will have in different effects in different parts of
Asia, like in China, India and Pakistan. Mean warming b/w 1999 to 2099 in South East Asia 2.5
°C, East Asia 3.3 °C, Central Asia &, Tibet 3.8 °C & North Asia 4.3°C. The precipitation will be
largest in North, East Asia and Central Asia, western parts of Asia. Summer rain increase in
North South, South East and East Asia and decrease in Central Asia (Solomon et al., 2007).
There will be also climate change in different parts of Africa, like temperature and
precipitation. From 1999 to 2099 i n West Africa, South Africa, East Africa & Saharan sub,
median temperature will increase with between 3 - 4 °C. Changing in the temperature of 3-4 °C
and 20% drying in Mediterranean and South Africa are predicted (Table 2.3). There are also
changes predited of the climate in Europe and Sweden. From 1999 to 2099 the annual mean
temperature in Northern Europe is predicted to increase with 2.2°C to 5.1°CPrecipitation
increases in north and decreases in South East, increases in Central Europe in winter are
predicted. A 70% increase in precipitation are predicted for mountainous areas of Scandinavian.
The mean air temperature in northern Sweden during spring and summer is expected to increase
1-2 degree centigrade 2000-2050. The precipitation willincrease 10-30% in winter and fall, but
not in spring and summer (Solomon et al., 2007).
24
Methane and tropospheric ozone are both key components driving climate change and
atmospheric chemistry (Dentener et al., 2005). Climate change policies focus mostly on CO 2
emissions reductions, although within Kyoto protocol, CH 4 and other greenhouse gases. Ozone
is not a part of Kyoto protocol (Dentener et al., 2005). Conventional air pollutant emissions
affect climate directly (through O 3 and aerosol production) and indirectly through their influence
on the CH 4 lifetime. IPCC SRES A2 emissions scenario showed global mean surface O 3
increases of about 5 ppb by 2020 and 20 ppb b y 2100 ( Dentener et al, 2006). How is climate
change expected to influence these ozone changes? The average results of 10 m odels for the
CLE 2030 scenario indicate that climate change may reduce surface O 3 by 1-2 ppb ove r the
oceans and by 0.5 ppb over the continents, although some regions, such as Eastern United States
(Dentener et al., 2006). Some quantities modelling studies have been performed. These include
effects related to changes in chemistry (via changes in temperature or water vapour), emissions
(e.g., biogenic VOC, lighting and soil NOx, wetland methane, and wildfires), and dynamics (e.g.,
convective mixing, precipitation, stratosphere-troposphere exchange, and boundary layer
ventilation) (Raes & Hjorth 2005). Climate–driven increases in temperature and water vapour
tend to decrease surface O 3 in the cleanest regions but tend to increase O 3 in more polluted areas.
A larger influx of stratosphere O 3 into the troposphere leads to a general increase of free
tropospheric O 3 (Dentener et al., 2006).
4.3 Which kind of interaction between ozone versus climate change and elevated CO 2 are
likely in these regions?
There are many ways in which the impacts of ozone on vegetation globally may be modified by
changing CO 2 levels. Climate, insect distributions, nutrient availability etc are examples. Global
climate change and ozone pollution share some of the anthropogenic causes, but has different
properties and differs impacts. The elevated CO 2 preventsome adverse effects of ozone on
vegetative growth of winter wheat but there was additional effect of ozone on grain yield on
which elevated CO 2 had no effect (Ashmore, 2005). When ozone is combined with elevated
CO 2 , yield loss is considerably less than with ozone alone (Fuhrer, 2009). Ozone increases grain
protein concentration on wheat while the protein yield will decrease. The effect of CO 2 on grain
quality is opposite to that of ozone (Fuhrer, 2009). Ozone alone had no ove rall effect on
concentrations of carbohydrates or nutrients in some experiments while in other a de crease in
concentration of carbohydrates and an increase in concentration of nutrients have been observed.
With a combination of elevated CO 2 and elevated O 3 reduced nutrient concentrations and
increased carbohydrates concentrations (Valkama et al., 2007). Elevated CO 2 reduces or
exacerbated the detrimental effects of O 3 . Increased carbon dioxide and ozone levels can both
lead to stomatal closure, reduces either gases, and in turn limits the damaging effect of ozone and
carbon dioxide fertilization of photosynthesis (Sitch et al., 2007).
Elevated ozone in combination with CO 2 increased terpene concentrations even more than
elevated O 3 alone, indicating an exacerbation of O 3 effects by elevated CO 2 (Valkama et al.,
2007). M eta-analysis demonstrated that effects of elevated O 3 in combinations with elevated
CO 2 on primary metabolites of trees were similar to the effects of elevated CO 2 alone (i.e.
nutrient concentrations were decreased, while concentrations of carbohydrate were increased).
Increasing atmospheric CO 2 concentrations will increase carbon-based secondary compounds
(CBSC; i.e. phenolics and terpenes) . This was because the magnitude of terpene response to O 3
25
plus CO 2 was larger than the magnitude of response to O 3 alone and CO 2 alone (Valkama. et al.,
2007). In some cases, carbon dioxide mitigated ozone effects (for example, carbohydrates in
angiosperm trees, phenolics and development time of insects herbivores), whereas for other
variables (nutrients in some tress species and terpenes), CO 2 exacerbated ozone effects (Valkama
et al., 2007).
Changing climatic conditions, stomata response to increased levels of CO 2 plays central role
for ozone risk to plants. Average reduction in stomatal conductance (g s ) by elevated CO 2 (475600 ppm) was predited to be 20 % until 2050 (IPCC 2007). General reduction in g s due to the
elevated CO 2 to reduce the ozone flux from the atmosphere to the plants interior can be
expected. Air pollutants like O 3 , SO 2 and NO x emitted from power station in china results
showed that average leaf CO 2 assimilation rate of citrus trees was 55% lower in polluted area
then in clean area (Emberson et al., 2003). Sitch et al. (2007) suggested that the resulting indirect
radiative forcing by ozone effects on pl ants could contribute more to global warming then the
direct radiative forcing due to CO 2 . Increase in global gross primary production (GPP) in 2100,
by physiological effects of elevated CO 2 , is prediced to be reduced by between 15.6 Pg Cyr-1 and
30.0 Pg Cyr-1. for plants with low and high ozone sensitivity. CO 2 -induced stomatal closure is
found to offset O 3 -suppression of GPP by over one-third, such that GPP by 2100 is 8-15% lower
due to O 3 exposure, rather than 14-23% lower in absence of CO 2 increases (Sitch et al., 2007).
4.4 How will these interactions affect the productivity and carbon sequestration of plants in
these regions?
Assessments of future ozone risks should include the complexity of the interactions between
vegetations, climate and ozone. However, the continuously ongoing agro-technological
developments with introduction of new crops and varieties, partly as a response to climate
change, future agro-ecosystems, and sensitivity to ozone and other stresses makes predictions
difficult (Fuhrer, 2009). Ozone enters to leaves through stomata. Via the production of reactive
oxygen species (ROS), it impairs photosynthesis and CO 2 fixation by impairing stomata
functioning and chlorophyll degradation specially leaves formed during flowering (Fuhrer,
2009). Effects of ozone on residue mass, the C/N ratio, decomposition processes in soil, reduced
rates of litter decomposition and transfer of C to roots, soil and soil C turnover. Data from study
with black burry and broomsedge bluestem indicated that ozone influences substrate quality and
soil microbial activity (Fuhrer, 2009).
In many trees like aspen and mixed aspen-birch it was observed that after 4 years of exposure,
ozone strongly inhibited extra stable soil C formation from elevated CO 2 . Ozone effect is high
on C pools in grassland soils, which probably contribute more than 10% of the total biosphere C
storage and reduced transfer C to soil. Moreover, effects of climate change, CO 2 and ozone on
soil C overlaps with strong effects of soil use and management (Fuhrer, 2009). The period 19002100, changes in O 3 with all other forcing fixed to reduce land-carbon storage accumulation by
between 143 Pg C and 263 Pg C.
In the Northern Hemisphere, ozone levels in the troposphere have increased by 35 pe rcent
over the past century, with detrimental impacts on f orest and agricultural productivity, even
when forest productivity has been stimulated by increased carbon dioxide levels. Increased
26
tropospheric ozone levels could alter terrestrial carbon cycling by lowering the quantity and
quality of carbon inputs to soils, e.g. in aspen stand and mixed aspen–birch stands. Results
suggest that, in a world with elevated atmospheric carbon dioxide concentrations, global-scale
reductions in plant productivity due to elevated ozone levels will also lower soil carbon
formation rates significantly (Loya et al., 2007).
Conclusions:
The main conclusions from this study are:
CO 2 -induced stomatal closure is likely to protect plants against ozone injury and might result in
higher atmospheric O 3 concentrations (which can influence human health) in a future
situation with more elevated CO 2 concentrations.
O 3 -induced stomatal closure and O 3 damage to photosynthesis/growth will limit the CO 2 fertilization effect and result in higher CO 2 concentrations in atmosphere.
Control measures of NO x and VOCs in North America, Japan and Europe, are likely to reduce
peak ozone concentrations, but still increases in O 3 concentrations are likely to persist in
parts of Asia, Latin America and Africa and intercontinental transport of ozone and its
precursors will become increasingly important as well as rising background ozone
concentrations over wide geographical areas.
The predicted future changes in ozone concentrations, exposure patterns and global distribution
of ozone are considered as important components of global change.
Ozone is expected to mostly affect vegetation in those areas, where the climatic conditions are
favourable for the formation of ozone, and where the climate promotes stomatal uptake of
ozone, such as in some parts of Asia, Latin America and Africa.
Ozone hazard for plants and crops depends on e xposure, ozone uptake by leaf and the plant’s
defence system.
In this review paper I emphasised that in some parts of the world increasing tropospheric ozone
concentrations can be expected over the next century, with potential for increasing the
current tropospheric ozone concentration, effects on vegetation and climate change.
In the present century, ozone effects on vegetation may be strongly modified by climate change:
in those areas where precipitation is increased ozone effects may become larger by
promotion of gas exchange, while in other parts of world dryer areas will be less affected by
ozone.
Further research and continuous studies will be important to identify ozone effect on vegetation
and areas under the influence of ozone, CO 2 and climate change in the future.
27
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