Children’s models of the ozone layer and ozone depletion1

Vasilia Christidou and Vasilis Koulaidis

University of Patras

Abstract

The views of forty primary students about ozone and its depletion were recorded through individual, semi-

structured interviews. The data analysis resulted in the formation of a limited number of models concerning i)

the distribution and role of ozone in the atmosphere, ii) the ozone depletion process, and iii) the consequences of

ozone depletion. Children’s models involve a variety of alternative conceptions which indicate the presence of a

number of different target obstacles, that is, critical factors constraining children’s understanding and thus

preventing the construction of adequate models. Five target obstacles were identified: a) the lack of conceptual

distinction between ultraviolet and other forms of solar radiation, b) the lack of the absorption mechanism of

ultraviolet rays by ozone, c) the conceptualisation of the atmosphere as an entirely homogeneous mixture of its

constituent gases, d) the non-localisation of the ozone layer around the earth, and e) the lack of interpretation of

the ‘ozone hole’ as a decrease in the concentration of ozone. The identification of those target obstacles

constitutes the first step for the design and evaluation of appropriate teaching aims and material.

Introduction

An understanding of the environmental problems and an estimation of their causes and possible

trends is a prerequisite for developing appropriate decision making and problem solving skills in future

citizens. Indeed, environmental issues, such as ozone depletion, are conceived by society to be of

increasing importance. This is evidenced by their wide coverage in mass media as well as by the fact that

they have started to appear in school curricula.

As considerable educational research (Pfundt & Duit, 1994) has shown pupils’ ideas concerning

a wide variety of scientific concepts differ considerably from either the scientifically accepted view or the

school version of scientific knowledge. These ideas are related to the every day life knowledge (Koulaidis

& Kouzelis, 1990; Matthews, 1994). Thus, one should first determine the pupils’ conceptions of these

issues in order to design and evaluate effective curricula and teaching material. From the standpoint of

science education the incorporation of environmental issues, such as ozone depletion, in science curricula

1 The final version of this paper was published in Research in Science Education, 26(4), 421-436.

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 2

would contribute to making science lessons more relevant and topical (Brody, 1994) by relating them to

real and important situations (Bybee, 1993), requiring an interdisciplinary approach (Iozzi, 1989).

However, it is only lately that children’s ideas of the ozone layer and depletion have started to

concentrate the interest of researchers (Boyes & Stanisstreet, 1993; Francis, Boyes, Qualter &

Stanisstreet, 1993; Plunkett & Skamp, 1994; Rye, Rubba & Wiesenmeyer, 1994; Christidou, 1996).

According to the results reported so far, ozone is considered to be a natural protective mechanism of the

earth against the harmful effects of sun rays by blocking part of them (Plunkett & Skamp, 1994;

Christidou, 1996). It seems to be a fairly common view among pupils that the ozone layer protects the

earth from getting too warm, while only very few children connect it with ultraviolet radiation (Plunkett

& Skamp, 1994). The depletion of ozone in the atmosphere is thus considered an environmental issue

(Plunkett & Skamp, 1994; Christidou, 1996), and is generally attributed to various (mainly manmade)

gases released on earth which pollute the atmosphere (Plunkett & Skamp, 1994; Francis et al., 1993; Rye

et al., 1994; Christidou, 1996). The action of these gases on ozone creates the ‘ozone hole(s)’ that let

more sunlight reach the planet (Plunkett & Skamp, 1994; Christidou, 1996). This increase in incident

radiation is believed to affect living organisms mainly by causing skin cancers (Plunkett & Skamp, 1994;

Boyes & Stanisstreet, 1993; Christidou, 1996). Also, another wide-spread conception attributes global

warming to ozone depletion, since the increased solar radiation reaching the earth is expected to warm up

the planet (Francis et al., 1993; Boyes & Stanisstreet, 1993; Rye et al., 1994; Plunkett & Skamp, 1994;

Christidou, 1996).

The aim of this paper is twofold:

a. To present the results concerning the way primary school children understand ozone layer depletion.

Specifically, we are going to focus on the models children seem to adopt in order to explain: i) The

position and the role of ozone in the atmosphere; ii) the process of ozone depletion and iii) the

consequences of ozone depletion.

b. To draw educational implications by taking into account the critical alternative conceptions children’s

models involve. In order to account for the emergence and persistence of these alternative conceptions we

indentify the relevant target obstacles. Target obstacles are factors that constrain pupils’ thinking

(Martinand 1982), thus preventing them from developing an adequate understanding of the ozone layer

and depletion and enhancing the construction of less accurate models. Thus, the identification of the

central target obstacles related to those issues can be a valuable educational tool for curriculum design.

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 3

Research method

For the purposes of the research 40 primary school children from 3 state urban primary schools

in the city of Thessaloniki were interviewed. It should be noted that the schools were located in different

borroughs and so the children of our sample came from a wide variety of social strata. Twenty two of the

pupils were boys and 18 were girls, while 13 were in the Fifth Grade (approximately 11 years old) and 27

in the Sixth Grade (approximately 12 years old). For the selection of pupils to be interviewed we relied on

the views of their teachers. The teachers were asked to choose pupils who in their opinion were average in

terms of performance and abilities. The sample is described in Table 1.

Table 1

Distribution of the pupils examined in regards to grade and gender.

Boys Girls Sum

Fifth grade 6 7 13

Sixth grade 16 11 27

Sum 22 18 40

It should be noted that the pupils had received no formal teaching concerning the ozone layer

and depletion prior to interviews.

For the data collection, individual semi-structured interviews were used. Each session comprised

two interviews and lasted for 60-70 minutes. The first interview was designed to set the context of the

discussion. For this purpose pupils were presented with material involving popularised scientific

information about the greenhouse effect and the ozone layer and its depletion. The second interview

constituted the main core of the session. During this part of the discussion, children had the opportunity to

express their views of the main causal relationships, interactions and overall mechanisms involved in the

issues under consideration. The interviews were designed in such a way as to prompt an in-depth and

detailed consideration of the central scientific processes, an analysis of them to their constituent parts, and

subsequent reconstruction of the whole picture by synthesising the main causal relationships and

explanations previously expressed.

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 4

The interviews were all recorded and transcribed. Transcripts were then condensed by isolating

all sentences which were referring to the following matters: i) The position and role of ozone in the

atmosphere, ii) the ozone depletion process, and iii) the ozone depletion consequences. For this treatment

of the data two people worked independently and found differences in only three cases. These differences

were resolved by the pupils’ teachers who were asked to say whether they thought that the pupils’

sentences contained relevant information or not. Based on the ‘condensed’ version of the transcripts we

developed children’s models, by classifying their views:

a) Regarding the position of ozone; this category includes three different options, since ozone can be

localised i) in a layer around the earth, ii) in a layer around the sun, or iii) uniformly distributed in the

atmosphere.

b) Regarding the role of ozone; this category is further subdivided in two alternative options. Thus, ozone

is either i) conceived to be stopping UV radiation (by blocking, absorbing, or filtering it), or ii)

thought to be reflecting the sun’s ultraviolet rays.

c) Regarding the nature of ozone depletion; the term ‘ozone hole’ can be conceptualised either i) as

absence, or complete destruction of ozone, or ii) as a decrease in the amount of ozone (decrease in

ozone concentration, or thinning of the ozone layer).

d) Regarding the consequences of ozone depletion; in this case the models were developed by taking into

account i) the consequences stated by pupils, ii) the position of the ozone layer, and iii) the way

ultraviolet rays pass through the ozone hole.

Results

The presentation of the results concerning the ozone layer and its depletion is structured as

follows. First, the models concerning the position (or distribution) of ozone in the atmosphere and its role

(models I.1, I.2, II.1, II.2, and III) are presented. The presentation of results continues with the pupils’

models of ozone depletion (models IV.1, IV.2, IV.3, V, VI, and VII). Finally, models regarding the ozone

depletion consequences are introduced (models VIII, IX, X, and XI). The models presented in the

following paragraphs are followed by their schematic representations and quotes illustrating them.

Since the specific types of solar radiation referred to by pupils constitute a fundamental element

of the models, they are distinctively represented, following the notation of figure 1.

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 5

Figure 1. The notation used to represent different kinds of radiation

The distribution and role of ozone in the atmosphere

Five distinct models were formed regarding the distribution of atmospheric ozone and its role.

All these models are presented below:

Model I.1: Ozone forms a layer at a large altitude above the earth. This layer stops the ultraviolet solar

radiation (or the dangerous sun rays in general), thus preventing it from reaching the earth.

The particular mechanism of this blockage was described by the pupils through a variety of

terms, for instance weakening, imprisonment, or absorption of the UV radiation, or simply

protection from this kind of harmful radiation. Model I.1 is illustrated in Figure 2.

"Ozone is a gas, it is a protective layer surrounding all the

earth and it doesn’t let the ultraviolet rays of the sun to pass. It

absorbs them and so it does not let them come to earth". (p19,

boy, 11 years)

Model I.2: Ozone forms a layer high in the atmosphere around the earth. The ozone layer reflects, or

scatters the ultraviolet rays, thus preventing them from entering the earth. The most central

elements of Model I.2 are represented in Figure 3.

"Ozone is like a cover that covers the earth. Like an

invisible umbrella, 25 kilometers above the ground. It

reflects the ultraviolet rays coming from the sun". (p6, boy,

12 years)

ultraviolet rays (UV)

solar rays

thermal rays, or heat (IR)

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 6

Figure 2 . Model I.1 Figure 3. Model I.2

Model II.1: Ozone is one of the atmosphere's ingredients, uniformly distributed in it. This gas has

the property of capturing the sun's ultraviolet (or harmful) rays, stopping them from

reaching the earth. An illustration of this model appears in figure 4.

"Ozone is in the atmosphere; it stops the ultraviolet rays

from coming to earth. [...] It helps the atmosphere to

absorb the harmful rays". (p3, girl, 11 years)

Model II.2: Ozone is an atmospheric ingredient, uniformly spread in the air around the earth.

However, the distinction between the ozone and atmosphere is not clear, since the

concepts are sometimes used alternatively in the same discussion. As can be also seen in

the model’s illustration in figure 5, ozone reflects the ultraviolet radiation coming from

the sun, while on the other hand it lets the sun’s thermal rays pass and reach the ground.

"The atmosphere is in the lower layers of the ozone. [...]

The atmosphere is made of ozone and it sends away the

sun’s ultraviolet rays. But it lets the sun’s thermal rays to

come in". (p17, girl, 12 years)

UV

UV

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 7

UV

UV

IR

Figure 4. Model II.1 Figure 5. Model II.2

Model III: Ozone forms a layer, 25 km above the earth. The ozone layer surrounds the sun,

stopping the ultraviolet (or harmful) radiation and protecting living things from its

damaging effects. Model III is graphically represented in Figure 6.

"Ozone is a gas and it forms a layer around the sun, 25

kilometres above the earth, and it prevents the ultraviolet

rays from reaching the earth". (p38, girl, 11 years)

Figure 6. Model III Figure 7. Model IV.1

The ozone depletion process

The process of the ozone layer depletion was understood by children in terms of the following

alternative models.

Model IV.1: Various gases released on earth as a result of human activities rise in the atmosphere,

and when they reach the ozone layer, they destroy it at some points and escape in space.

(Although most of the children referred explicitly to CFCs as gases that damage ozone,

several also attributed the same role to carbon dioxide, methane, or smog in general.

UV

harmful

gases

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 8

The production of those gases and their release in the atmosphere is usually attributed to

human factors. The same applies to the subsequent models of ozone depletion). This

way, the ‘ozone holes’, areas where ozone has disappeared, are formed. An illustration

of Model IV.1 appears in Figure 7.

"CFCs, together with carbon dioxide and other gases, are

very strong: they pollute the atmosphere and make many

little holes in the ozone layer". (p5, girl, 11 years)

Model IV.2: Harmful gases, while rising up in the atmosphere, form layers that displace the ozone at

some points of the layer. The result of this interaction is the emergence of ‘ozone holes’,

areas where there is no ozone. The particular features of Model IV.2 are illustrated in

Figure 8.

"[...] These gases rise in the atmosphere in layers and

destroy the ozone, kill it, make the ozone holes". (p14, boy,

12 years)

Model IV.3: After passing through ozone, the gases can continue their upward motion, but they can

also change their direction, passing through the layer for a second time. This destroys

even more ozone, making the hole even bigger. Figure 9 graphically represents this

model.

"CFCs make a hole in the ozone layer and from there they

go out to space. But then they can come back in through the

ozone hole, making it even bigger". (p10, boy, 11 years)

Figure 8 . Model IV.2 Figure 9. Model IV.3

harmful

gases

harmful

gases

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 9

Model V: Various man-made gases released on earth, interact with ozone, destroying it and

altering the atmosphere’s composition. The term ‘ozone hole’ is interpreted as a

decrease in the concentration of ozone in the atmosphere. The particular features of this

model are illustrated in Figure 10.

"When CFCs and methane are produced, the atmosphere

changes. So the ozone changes too, it is being destroyed; in

this way the ozone hole is created". (p1, boy, 12 years)

Model VI: CFCs and other gases produced on earth, as a result of human activities, rise up in the

atmosphere, and finally reach the ozone layer surrounding the sun. There they destroy

ozone, making holes in its layer. Ozone holes are described as areas with no ozone.

Figure 11 represents Model VI.

"The sun helps CFCs to evaporate, and they leave the earth

and they go to the ozone layer. There they irritate ozone

and destroy it... that is they make the ozone hole". (p11,

girl, 11 years)

Figure 10. Model V Figure 11. Model VI

Model VII: Various gases, mainly released by human activities, affect the ozone layer surrounding

the earth. The ozone holes are described in this case as areas where the concentration of

ozone decreases, or as has been alternatively expressed in some cases, its layer becomes

thinner. Model VII is represented in Figure 12.

harmful

gases

harmful

gases

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 10

"CFCs rise up, and they go into the layer made of ozone

and there they dilute it, they make it less dense". (p7, boy,

11 years)

Figure 12. Model VII

The ozone depletion consequences

Regarding the consequences of the depletion of ozone, the data analysis resulted in four distinct

models, following the main categories of the two previous paragraphs. These models are illustrated

below.

Model VIII: As can be also seen in Figure 13 representing this model, more ultraviolet rays (or

sunlight) can pass through the holes in the ozone layer and reach the earth. Ultraviolet

rays are usually considered to be very strong, hence very hot, so they warm up the

planet and can melt the polar ice. Ultraviolet radiation is also considered especially

harmful for all living organisms.

"The sun’s ultraviolet rays pass through the holes in the

ozone layer and they can damage people; they cause big

changes to our body. [...] Ultraviolet rays can change the

climate of the earth". (p31, girl, 11 years)

Model IX: As a result of the decrease in ozone concentration, the atmosphere loses part of its

capacity of blocking ultraviolet (or dangerous solar) radiation. Thus, more ultraviolet

rays can pass through the atmosphere and reach the earth. Those rays are described as

particularly harmful for plants and animals, but can also lead to a rise in the earth’s

temperature. Model IX is illustrated in Figure 14.

harmful

gases

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 11

"As the ozone is getting less dense, more ultraviolet rays

come in and they cause various diseases and the climate

changes because more heat is coming in" (p21, boy, 12

years)

UV

UV

Figure 13. Model VIII Figure 14. Model IX

Model X: Ultraviolet (or harmful) rays can pass unhindered through the holes in the ozone layer

around the sun and reach the earth. These rays are considered especially harmful for the

human health. The features of Model X are illustrated in Figure 15.

"Ultraviolet rays give us our summer tan; but as they pass

through the hole, because the sun is not protected very well

now, they can burn our skin and cause many diseases...

especially cancer" (p38, girl, 11 years)

Model XI: More ultraviolet (or harmful solar) rays can enter the atmosphere from the parts in the

ozone layer where ozone concentration has decreased or where the layer has become

'thinner' and reach the earth (Figure 16). This type of solar radiation is described as

extremely dangerous for the human health, as well as for all living things. Additionally,

ultraviolet rays are described as extremely hot, so they can rise the earth’s temperature

and affect its climate.

"The ozone in the layer is getting less and more sun rays

are coming to earth. They can burn us, they can warm the

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 12

climate; the icebergs in the poles will melt and the villages

that are near the sea will be flooded..." (p25, boy, 12 years)

Figure 15. Model X Figure 16. Model XI

Discussion of the results

Overview

Table 2 illustrates the models corresponding to the ozone distribution and role, the process of

ozone depletion and the ozone depletion consequences. The table also indicates the numbers and the

percentages of pupils adopting these models.

Children’s personal models reveal common patterns. The following paragraphs are concerned

with the elements of children’s thinking common in all models, as well as those that constitute the

distinguishing points among the specific models.

The distribution and role of ozone in the atmosphere

Regarding the ozone distribution and role in the atmosphere, five distinct models were formed.

The results indicate that primary pupils can understand the concept of an atmospheric layer that has the

property of blocking (in some way) the harmful solar radiation. This constitutes the primary (although

oversimplified) mechanism for the role of ozone. However, children did not refer to UV rays in a

consistent manner, and they often tended to use it as equivalent to the terms ‘sunlight’, or ‘heat’. This

element of children’s thinking is more clearly marked in the models concerning the ozone depletion

consequences (see below).

These general remarks complement results reported by other researchers concerning the

conceptualisation of the ozone depletion. Inaccuracies in the pupils’ use of the term ‘ultraviolet radiation’

concerning the role of ozone have also been reported by Plunkett and Skamp (1994).

UV

UV

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 13

Table 2

Models constructed from pupils’ answers and numbers of pupils adopting these models

Theme Model Number of pupils

adopting the model

Percentage

The distribution and role I.1 Ozone: layer that stops UV 30 71.43

of ozone in the I.2 Ozone: layer that reflects UV 3 7.14

atmosphere2 II.1 Ozone: uniform distribution and

blocking of UV

6 14.29

II.2 Ozone: uniform distribution and

reflection of UV

1 2.38

III Ozone: layer that surrounds the sun and

stops UV

2 4.76

The ozone depletion

process

IV.1 Man-made gases following upward

motion destroy the ozone layer locally

23 57.50

IV.2 Ozone depletion by layers of harmful

gases moving upwards

1 2.50

IV.3 Local destruction of the ozone layer

by gases in upward and downward

motion

1 2.50

V Ozone concentration decrease changes

atmospheric composition

6 15.00

VI Man-made gases moving upwards

destroy the ozone layer surrounding the

sun locally

2 5.00

VII Local decrease in the concentration of

ozone in the ozone layer

7 17.50

The ozone depletion

consequences

VIII UV rays pass through the hole in the

ozone layer unhindered

25 62.50

IX More UV radiation reaches the ground

because of the ozone concentration

decrease

6 15.00

X UV rays pass freely through the hole in

the ozone layer around the sun

2 5.00

XI More UV radiation enters the earth

from the areas with decreased

concentration of ozone in its layer

7 17.50

The ozone layer and depletion: a common ground in children’s views

Concerning the ozone distribution in the atmosphere, three models portrayed ozone as forming a

layer in the sky, surrounding the earth (models I.1 and I.2, 33 instances in total) or the sun (model III, 2

2 The number of pupils who adopted the models related to this theme is 42, since two pupils adopted two models/a double model

each regarding ozone and its role. In this case the corresponding percentages have been calculated based on this total of models recorded.

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 14

instances). Two models (models II.1 and II.2, 7 instances) described ozone as uniformly spread in the

atmosphere.

As far as the role of ozone is concerned, there is a strong preference for the mechanism of

blocking, or stopping ultraviolet radiation (models I.1, II.1 and III which amount to 38 instances) over the

process of reflection (models I.2 and II.2, 4 instances in total).

The ozone depletion process

The mechanism of the depletion of ozone in the atmosphere was approached by 6 distinct

models. A common view among all children was that ozone is being destroyed by man-made gases that

are released and can move freely in the atmosphere. Children referred to different gases (such as CFCs,

carbon dioxide, methane) or to "pollution" in general as factors that affect ozone. This confusion about

the causes of the ozone depletion and the causes of other environmental problems has also been reported

by other researchers (Rye et al., 1994; Plunkett & Skamp, 1994).

However, the present analysis is mainly concerned with the processes regarding ozone and its

depletion, thus the identity of damaging gases has not been used as a criterion in the formation of the

models.

Apart from the distribution of ozone in the atmosphere, the main distinguishing point among the

models concerning the role of ozone is the meaning children attributed to the term ‘ozone hole’. Thus, in

four models (models IV.1, IV.2, IV.3, and VI, 27 instances in total) the ozone hole was interpreted

literally, i.e. as an area in the ozone layer where ozone has been completely destroyed. In 13 cases,

however, children conceptualised the term ‘ozone hole’ metaphorically, explaining that in those areas

ozone is getting "diluted", or less dense, or that the ozone layer is getting thinner. Those views (held by

the pupils who adopted models V and VII, 13 instances in total) are in greater proximity to the scientific

meaning of the term, which denotes the ozone concentration decrease.

Plunkett and Skamp (1994) have also recorded literal uses of the ‘ozone hole’ as well as the

conception of the ozone layer getting thinner, but not the view of ozone concentration decrease. Our

results indicate that senior primary pupils can understand this metaphorical term, if appropriately

instructed.

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 15

The consequences of ozone depletion

Children’s explanations of the consequences of ozone depletion form 4 different models.

Children agree that the main consequence of ozone depletion is the increase of the ultraviolet, or harmful,

solar radiation reaching the earth.

Thus, according to models VIII and X (27 instances in total), ultraviolet rays enter unhindered

from the parts of the ozone layer where ozone has been completely destroyed. On the other hand, models

IX and XI (corresponding to 13 pupils in total) suggest that at the areas where ozone has become less

dense, or thinner, its capacity to stop UV rays has weakened. Thus, more ultraviolet radiation can pass

and reach the earth.

Two types of effects of the increased UV radiation due to ozone depletion were expressed: a)

this type of harmful solar radiation is biologically active, thus it is likely to affect the living organisms

causing various types of cancer (especially skin cancer), or other serious diseases; b) however, quite often

children attributed thermal properties to ultraviolet rays, suggesting that they are extremely strong, hence

very hot and thus they can change the climate and melt polar ice.

Moreover, it might be worth emphasising that while the properties of ultraviolet radiation were

confused with the properties of longwave infrared radiation (referred to as "heat"), no such correlation

was made with the properties of the visible spectrum (that is no pupil suggested that from the ozone hole

more light may come in, or that UV radiation is extremely bright). This suggests that, with regard to the

environmental issues discussed in the course of this research, 11-12 year-old children may perceive the

sun more as a source of heat than as a source of light.

These findings agree with those reported by Plunkett and Skamp (1994) and Francis et al.

(1993). These researchers suggest as possible explanations for such confusions a) that children may have

a generalised and unified view of global environmental issues, and b) that children consider ozone

depletion as a cause of global warming, thus connecting (or confusing) the two phenomena. However, we

suggest that the primary reason for the emergence of such limited and inaccurate conceptions regarding

ozone depletion and its consequences is that children have no knowledge of the different types of

radiation, with different properties, included in the solar spectrum. This lack of essential knowledge might

in fact lead to overgeneralisations as well as to the unification of different issues.

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 16

Teaching implications: target obstacles

Children’s models concerning the ozone layer, its depletion and the consequences of this

depletion involve a variety of alternative conceptions. However, the emergence of common patterns of

thinking among pupils (which made the construction of a limited number of models possible) permits the

identification of what we call ‘target obstacles’. Target obstacles have two prevalent features (Martinand,

1982):

a) they are important and central components of the processes concerning ozone and its depletion

with respect to which children’s thinking diverges from the scientific point of view, thus

preventing children from constructing adequate models, and

b) an appropriate introduction of those components should help to detach children’s thinking from

most of the common and critical alternative conceptions recorded by the present research, and

develop more adequate models of the processes involving ozone and its depletion.

Thus, the identification of the factors constraining children’s thinking permits at the same time

the selection of suitable teaching aims. Moreover, the number of different alternative conceptions taken

into account in order to formulate each target obstacle, as well as the number of the different models it

affects, constitute criteria of its importance.

The target obstacles identified by the present analysis are summarized in Table 3, and will be

presented in detail in the following paragraphs.

Target obstacle (i): Lack of distinction between UV and solar radiation

As already mentioned in the previous section, pupils did not refer to ultraviolet rays consistently.

Even when they did they made no explicit conceptual differentiation between this type of radiation and

sun rays, or thermal rays. This lack of conceptual distinction characterises all models concerning the

distribution and role of ozone in the atmosphere and the ozone depletion consequences, with the exeption

of model II.2 which describes ozone as acting selectively on different kinds of solar rays.

However, the specific nature, characteristics, and properties of ultraviolet radiation are

fundamental and indispensable elements for an adequate conceptualisation of atmospheric ozone. The

presence of target obstacle (i) might constitute the primary factor imposing a generalised view of different

environmental issues, and, more specifically, can lead pupils to confuse or causally connect ozone

depletion with global warming. Such confusions have been reported by all the researchers studying

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 17

pupils’ ideas on those two issues (Boyes & Stanisstreet, 1993; Francis et al., 1993; Rye et al., 1994;

Plunkett & Skamp, 1994; Christidou, 1996).

Table 3

Target obstacles identified in children’s models

Theme Model Target obstacle

Distribution and role

of ozone in the

atmosphere

I.1 Ozone: layer that stops UV (or harmful

solar radiation)

i. Lack of coherent conceptual

distinction between UV and

other forms of solar radiation

I.2 Ozone: layer that reflects UV (or

harmful solar radiation)

Target obstacle i and

ii. Lack of the absorption

mechanism of UV rays by

ozone

II.1 Ozone: uniform distribution, blocks

UV (or harmful solar radiation)

Target obstacle i and

iii. Atmosphere conceptualised

as an entirely homogeneous

mixture of its constituent

gases

II.2 Ozone: uniform distribution,

reflection of UV

Target obstacles ii and iii

III Ozone: layer surrounding the sun,

stops UV (or harmful solar radiation)

Target obstacle i and

iv. Ozone layer not localised

around the earth

The ozone depletion

process

IV.1 Local destruction of ozone by gases

in an upward motion

v. ‘Ozone hole’ not interpreted

as decrease in ozone

concentration

IV.2 Local destruction of ozone by layers

of gases in upward motion

Target obstacle v

IV.3 Local destruction of ozone by gases

in upward and downward motion

Target obstacle v

V Ozone concentration decrease by man-

made gases, altering atmospheric

composition

Target obstacle iii

VI Local destruction of the ozone layer

around the sun, by gases in an upward

motion

Target obstacle v

VII Local ozone depletion by man-made

gases in an upward motion

Target obstacle v2

The ozone depletion

consequences

VIII UV rays reach the earth unhindered,

passing through the ozone hole

Target obstacles v and i

IX Due to decreased ozone concentration

more UV radiation reaches the earth

Target obstacle i

X UV rays reach the earth unhindered,

through the hole in the ozone layer

around the sun

Target obstacles v and i

XI More UV radiation reaches the earth

due to ozone depletion

Target obstacle i

2 This target obstacle only concerns those cases in this model where the ‘ozone holes’ were conceptualised as parts of the

ozone layer where it has become thinner.

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 18

Target obstacle (ii): Lack of the absorption mechanism of UV by ozone

Children who adopted models I.2 and II.2 for the distribution and role of ozone described ozone

as reflecting ultraviolet radiation, thus sending it back to space. This is an inaccurate view that results

from the fact that pupils do not conceptualise ozone as an atmospheric gas that can absorb UV rays.

The mechanism of absorption of UV rays is in fact based on the continuous creation and

destruction of ozone in the stratosphere through the photolytic action of ultraviolet radiation on molecular

oxygen (Bojkov, 1995). Thus, an appropriate introduction of the mechanism of absorption in the context

of the role of ozone in the atmosphere should remove the alternative conception involving the reflection

mechanism.

Target obstacle (iii): Atmosphere conceptualised as entirely homogeneous

Target obstacle (iii) implies that atmosphere is a well - mixed, entirely homogeneous mixture of

its constituent gases, one of which is ozone. Ozone is seen as uniformly spread into the atmosphere by the

pupils who adopted models II.1 and II.2 for the ozone distribution and role, and model V for the ozone

depletion process.

What is missing in those models is that ozone presents its maximum concentration at an altitude

of 19-23 km above the earth where it is constantly created and destroyed through photolytic processes, as

described above (Bojkov, 1995). Introducing an accurate localisation for the ozone should help children

distinguish among ozone and the rest of the atmospheric constituents, and form more adequate

representations of the ‘ozone layer’.

Target obstacle (iv): Ozone layer not localised around the earth

The presence of target obstacle (iv) determines the formation of model III, according to which

ozone is localised in a relatively thin layer that surrounds the sun, and thus filters its harmful UV rays.

Target obstacle (iv) should be overcome by introducing a model describing ozone as a

constituent of the earth’s atmosphere, that forms a fairly localised layer at an altitude of about 20-30 km

around the earth, protecting it from the harmful effects of UV radiation (Bojkov, 1995; World

Meteorological Organisation (WMO), 1994).

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 19

Target obstacle (v): ‘Ozone hole’ not interpreted as a decrease in ozone concentration

The presence of target obstacle (v) can cause a literal interpretation of the term ‘ozone hole’,

which determines the formation of models IV.1, IV.2, IV.3, and VI concerning the ozone depletion

process, as well as the models VIII and X concerning the ozone depletion consequences. It is also

responsible for the alternative conceptualisation of the ozone depletion as a decrease in layer thickness,

recorded in some instances of model XI.

Target obstacle (v) can be removed if the concept of the ozone concentration decrease is

appropriately introduced. The ‘ozone hole’ is defined as a rapid and abrupt change in the stratospheric

ozone concentration over the Antarctic during early spring (September-October). Less intensely marked

ozone losses have been recorded during the last decade over the middle and polar latitudes in both

hemispheres. Although these global ozone declines cannot be characterised as ‘ozone holes’, they are also

attributed to anthropogenic halocarbons (Bojkov, 1995; WMO, 1994).

Conclusion

The present study shows that there is a common core of beliefs among primary school children

concerning the ozone layer and depletion. In particular, this common core involves views that can be

traced out across all models. Summarizing the common elements found in the models of the previous

section, children seem to believe that:

Ozone is a gas found in the atmosphere. It prevents ultraviolet (or harmful) solar radiation, which

is extremely dangerous for all living organisms, from reaching the earth. Ozone is being destroyed by

various gases released in the atmosphere as a result of human activities. The depletion of ozone affects its

capacity to filter the ultraviolet radiation. From the 'ozone holes' the sun's ultraviolet rays may enter the

atmosphere (almost) unhindered, causing skin cancers and harming all plants and animals. Ultraviolet

rays are also considered very hot, so they can warm up the earth and melt the polar ice.

On the other hand children’s views are differentiated in several ways. The differences among

children’s views concern a) the ozone’s distribution in the atmosphere, b) the mechanism preventing UV

radiation from entering the earth (when specified), c) the specific gases damaging ozone, d) the process of

ozone depletion, e) the meaning attributed to the ‘ozone hole’, f) differences in the degree of distinction

among different types of solar radiation, and g) the partial consequences of ozone depletion.

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 20

A limited number of models concerning i) the distribution and role of ozone, ii) the process of

ozone depletion, and iii) the consequences of ozone depletion were constructed. These models are fairly

structured and logical. The alternative conceptions these models involve lead to the identification of five

target obstacles that any teaching attempt concerning ozone should aim at overcoming:

target obstacle (i), which suggests the necessity of coherently introducing the conceptual

distinction between UV and solar radiation; overcoming this target obstacle should be

decisive in order to

a) clarify the role of the ozone layer in the atmosphere,

b) refute the conception that UV radiation is extremely warm and can cause climatic

changes, and

c) distinguish between ozone depletion and global warming (i.e. among the different

processes each phenomenon involves, the specific gases causing each of them and their

consequences)

target obstacle (ii), which refers to the need to appropriately introduce the process of

absorption of UV radiation by ozone; the achievement of this target obstacle, should help to

overcome the conception that ozone is a reflective medium, scattering ultraviolet radiation

target obstacle (iii), which implies the need to introduce the concept of an atmospheric layer,

(i.e. a relatively limited region of the atmosphere, with special composition and properties);

its achievement should help to overcome

a) the conceptualisation of ozone as uniformly distributed in the atmosphere, and

b) the conceptualisation of ozone depletion as a form of ‘pollution’, that alters the

atmospheric composition

target obstacle (iv), which designates the need to explicitly introduce the ozone layer’s

localisation around the earth; overcoming this obstacle should remove the alternative

conception of the localisation of ozone around the sun

target obstacle (v), which implies the need to clarify the metaphorical term ‘ozone hole’, by

interpreting it as local decrease in the ozone concentration; overcoming this target obstacle

should release children’s thinking from

a) the inaccurate, literal interpretation of the term, implying that the ozone hole is an area of

empty space;

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 21

b) the inaccurate conceptualisation of the ozone hole as a region where the ozone layer is

getting thinner, and

c) the conception that ultraviolet radiation passes through the ozone hole totally unhindered.

A combined examination of the above remarks with the contents of Table 3 leads to the

conclusion that target obstacle (i) is at the same time the most frequent and most significant of the

constraining factors limiting the understanding of the ozone depletion, since it is connected to three

alternative conceptions involved in eight models. Also, target obstacle (v) is responsible for the formation

of three alternative notions, characterising seven distinct models.

CHILDREN’S MODELS OF THE OZONE LAYER AND DEPLETION 22

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