Journal of Environmental Protection, 2010, 1, 374-383
doi:10.4236/jep.2010.14043 Published Online December 2010 (http://www.SciRP.org/journal/jep)
Status of Stratospheric Ozone over Pakistan
1987-2008
Maida Zahid, Ghulam Rasul
Research & Development Division, Pakistan Meteorological Department, Islamabad, Pakistan.
Received June 29th, 2010; revised September 1st, 201 0; accepted Septembe r 5th, 2010.
ABSTRACT
The ozone layer depletion and its harmful impact on living beings have been a greater concern of all the scientists all
over the world. The aim of this paper is to reveal the current status of stratospheric ozone over Pakistan. The annual,
monthly and seasonal analyses have been performed in order to check the status. The variation in total column of ozone
has been observed during these analyses and decrease in total column of ozone has been seen in all the investigations
from 1987-2008. Th e correlation coefficient for JRA forecasted data and ob served ozone data is 0.6. Both the data sets
show decline in ozone concentration. The total change calculated in annual depth of ozone is −5.67 D.U and −4.2 D.U
in monthly depth of ozone. The seasonal analysis shows that the total change in ozone in summer is −6.3 D.U, in spring
−10.5 D.U, in winter −3.15 D.U and in autumn −2.0 D.U. Maximum change in ozone thickness has been found in
spring and minimum in autumn. The solar radiations, decrease in temperatures of stratosphere and carbon dioxide
(CO2) play significant role in o zone layer depletion. Accord ing to the findings of this stud y solar radiatio ns and carbon
dioxide (CO2) are inversely proportional to the total column of ozone. The correlation coefficient for solar radiations
and ozone on annual basis is 0.44 (R2 = 0.44) and on monthly basis is around 0.35 (R2 = 0.35). Therefore the more
intense the solar radia tions the more ozone layer thinning will occur. The correlation coefficien t for ozone and carbon
dioxide is around 0.3 (R2 = 0.3) during the study period. The decrease in stratospheric temperatures will cause the
cooling of stratosphere which is ultimately responsible for ozone layer depletion. The total decrease analyzed in
stratospheric temperatures during the study period is about −1.3℃. It is observed that alarming rise in carbon dioxide
(CO2) concentration is not only contributing to global warming in troposphere but cooling in the stratosphere.
Keywords: Oz one Layer Depletion, Stratosphere, Greenhouse Gases GH G’s and Solar Radiation
1. Introduction
Ozone layer plays an extremely important and manifold
role in terrestrial life and particularly in the life of human
beings. The 90% of atmospheric ozone is contained in
the ozone layer, which shields the earth by absorbing
harmful ultraviolet radiation from the Sun. Ozone con-
centration can vary over extremely wide limits at a given
spatial location, with time [1]. The stratosphere plays an
important role in the climate system. The ozone present
in the stratosphere results from a balance between pho-
tochemical processes producing and destroying it. The
processes of production involves rather fast interactions,
between short wavelength UV (250 nm) from the sun and
normal oxygen (O2) in the upper stratosphere [2]. These
catalytic reactions occur above 25 Km. Since neither the
strength of the sun’s radiation nor the amount of normal
oxygen in the atmosphere can be changed by human in-
tervention; therefore they can not alter the production
rate. Both destruction and production processes in the
stratosphere take place on a very short time scale and in
the presence of short wavelength UV.
The destruction processes of ozone in the stratosphere
are due to the presence of number of free radical cata-
lysts, the most important of which are the hydroxyl radi-
cal (OH·), the nitric oxide radical (NO), atomic chlorine
(Cl) and bromine (Br). All of these have both na tural and
manmade sources. Currently the OH and NO are of
natural origin in the stratosphere, where NO contribute
70% of it in destruction of ozone. While anthropogenic
activities have severely increased the levels of chlorine
and bromine. These elements are found in certain stable
organic compounds, especially chlorofluorocarbons
(CFCs), which reaches the stratosphere without being
destroyed in the troposphere due to their low reactivity
where they liberated Cl and Br atoms by the action of

Status of Stratospheric Ozone over Pakistan 1987-2008 375
ultraviolet light as shown in Figure 1. However an in-
crease of about 30% for Cl, source strength or a decrease
of about 30% for NO, source strength from their current
level may lead to catastrophic transition and results in a
reduction of ozone concentration about 50 times [3].
The total amount of overhead ozone is an important
quantity, as it determines the penetration of UV-B to the
earth’s surface. Circulation disturbances change the
ozone distribution by their vertical and horizontal advec-
tion [4-5]. The distribution of ozone between tropopause
and 30 Km is controlled by atmospheric and strato-
spheric transport. Ozone is 260 D.U near the equator,
while it between 300-350 D.U at mid latitudes and at
poles its concentration varies from 450-500 D.U [6].
The ozone concentration is sensitive to significant
daily, seasonal and interannual fluctuations and tends to
be highest in late winter and early spring [7-10]. The
Total Ozone Mapping Spectrometer (TOMS) satellite
measurements are monitoring total ozone content (TOC)
in the atmosphere nowadays. The data of ground based
ozone stations supplement and refine the satellite meas-
urements and yield information about regional features in
TOC variations. The decrease in total ozone content has
been observed over central Eurasia from 1980-2003 at an
average rate of −1.29 ± 0.08 DU/ yr [11].
The ozone is transported to Pakistan atmospheric re-
gions due to the geograph ical position and the large posi-
tive correlation between the potential vo rticity deviations
and the ozone mixing ratios in the stratosphere [12]. The
ozone that has been transported to Pakistan’s atmos-
pheric region by means of vertical lifting and horizontal
shifting has also shown decreasing trends over Pakistan
(West or Northwest of South Asia having latitude
23.45ºN-36.75ºN and longitude 61ºE and 75.5ºE) from
1979-1993 by comparing TOMS satellite data and Dob-
son spectrometer ground observation data. Both the data
sets have shown sharp decline in ozone layer thickness
over Pakistan [13-14]. The long-term effect of ozone
layer depletion appears to be an increase in the ultraviolet
radiation reaching the earth. But the intensity of UV ra-
diations varies with the thickness of ozone. Therefore the
filtration of UV flux due to variation in ozone layer is
still unanswered [1]. The effect of ozone layer depletion
over marine life, forests and human beings have been
studied by different scientists all over the world [15-17]
But the annual, monthly and seasonal analysis of ozone
layer over Pakistan using observed Dobson spectrometer
data have not been do ne yet .
The aim of this paper is not only to find out the annual,
monthly and seasonal behavior of ozone over Pakistan
but also to calculate the average change in total column
ozone thickness in each of these analyses. The ozone
layer thickness depends on some of the atmospheric
variables like temperature and solar radiations. The stra-
tosphere has been cooling in recent decades and changes
in stratospheric ozone, greenhouse gases (GHG), water
vapor and Sea Surface Temperatures (SSTs) all contrib-
ute to this cooling [18-22]. Therefore the relations be-
tween these parameters including CO2 and ozone have
also been done in this study.
2. Methodology
The World Meteorological Organization (WMO) has
installed a Dobson Spectrophotometer at Geophysical
Center, Pakistan Meteorological Department, Quetta for
monitoring the data of Ozone depth for Pakistan’s at-
mospheric region Figure 2. The Dobson ozone spectro-
photometer measures the relative intensities of transmit-
ted sunlight, at two different wavelengths in the UV, one
being strongly and other being weakly absorbed by
ozone to determine the total amount of ozone overhead.
The real time data of mean monthly total column ozone
and solar radiations for a period 1987-2008 is obtained
from Geophysical Center, Quetta in order to calculate the
current status of stratospheric ozone over Pakistan.
The Japan Meteorological Agency (JMA) conducted
the Japanese 25-year Reanalysis (JRA-25) in collabora-
tion with the Central Research Institu te of Electric Power
Industry (CRIEPI) and produced high quality meteoro-
logical datasets for seasonal prediction models and cli-
mate research use. The monthly mean values of Tem-
perature at different levels (1000 hPa, 850 hPa, 700 hPa,
500 hPa, 300 hPa, 100 hPa 50 hPa and 15 hPa) and
ozone has been extracted with the help of Japanese re-
analysis data (JRA) for the study period using software
GrADS (The Grid Analysis and Display System).
The Carbon Dioxide Information Analysis Center
(CDIAC) is the primary climate-change data and infor-
mation analysis center of the U.S. Department of Energy
(DOE) since 1982. They generate data at global, regional
and national scale. Carbon dioxide emissions data for
Pakistan has been obtained from Carbon dioxide Infor-
mation Analysis Data Center (CDIAC) from 1987-2007.
3. Results & Discussion
3.1. Annual Analysis
The annual analysis of total column ozone data has been
done by generating a time series for the period 1987-
2008. The time series shows that there is a sharp decline
in the thickness of ozone layer particularly from 1993
onwards over Pakistan. The time series of forecasted
total column ozone Japanese Reanalysis Data (JRA) has
further supported the evidence of ozone layer thinning in
the region of Pakistan Figure 3. A comparison between
two data sets has been made which portray a strong

Status of Stratospheric Ozone over Pakistan 1987-2008 376
Figure 1. Representation of the processes that determine the concentration of ozone in the atmosphere.
Figure 2. Map showing the location of total ozone stations around the world.

Status of Stratospheric Ozone over Pakistan 1987-2008 377
Figure 3. Time series of average annual observed & JRA ozone data 1987-2008 over Pakistan.
Figure 4. Inter-annual ozone anomalies 1987-2008 observed at Geophysical Center Quetta.
positive correlation between observed and predicted data
of ozone. The correlation coefficient for both the data
sets is around 0.6 (R2 = 0.6).
Figure 4 shows the change in annual depth of total
column zone in the atmosphere of Pakistan. The annual
ozone anomalies have been calculated with the help of
observed data. The anomalies show decreasing trend of
ozone and this loss in total colu mn ozone give a clue that
ozone layer thickness has reduced and thinness has in-
creased during the study period. The total change ob-

Status of Stratospheric Ozone over Pakistan 1987-2008 378
Figure 5. Monthly status of ozone over Pakistan 1987-2008.
served in ozone over the last 21 years (1987-2008) is
−5.67 D.U. It is assumed that this decrease can be due to
huge gaseous emissions of Carbondioxide (CO2) and
particularly Chlorofluorocarbons (CFC’s) which is the
main cause of ozone de pl et i o n ov e r Paki st an.
3.2. Monthly Analysis
The monthly analysis of ozone shows a lot of variations
in ozone thickn ess throughout the year . There ar e months
in which the ozone thickness remains far above the per-
missible limits of ozone (i.e. 260 D.U. in tropics near
equator) whereas on the other hand, there are few months
when the ozone layer becomes thin and the value of
ozone calculated below the 260 D.U. The highest
amounts of total column ozone over Pakistan occur from
March–May, the amount then starts to decrease from
June–September. While the lowest amount of total col-
umn ozone occurs from October–December, the amount
of zone then again increases from January–February
Figure 5. The wind transport of ozone is principally re-
sponsible for this monthly variation of ozone patterns.
Figure 6 shows the total change in thickness of
monthly ozone and decreasing trend of ozone over Paki-
stan’s atmosphere from 1987-2008. The monthly ozone
anomalies show that ozone layer thinness has increased
during the study period. The total decrease in ozone
thickness is −4.2 D.U which is statistically significant at
95% confidence level. The change has been calculated
with the help of straight line equation y = mx + c. In this
equation multiplying ‘m’ or ‘slope’ with total number of
years will give the total change during the study period.
3.3. Seasonal Analysis
Pakistan has four seasons; a cool, dry winter starts from
Dec and en ds in Feb; a hot dry spri n g fr om Mar to M a y ; a
hot, rainy summer season or south west monsoon period
from J un to Sep a nd autumn o f Oct and N ov. The behav ior
of ozone varies from season to season. Since the strato-
spheric ozone is produced by the UV radiation, therefore
Figure 6. Ozone monthly anomalies monitored at GC Quetta from 1987-2008.

Status of Stratospheric Ozone over Pakistan 1987-2008 379
the highest concentration of ozone levels must be found
over tropics and the lowest over the Po lar Regions which
consequently lead to highest ozone level in summer and
the lowest in the winter. But this is not the case; the ob-
served behavior is quite different. The highest level of
ozone occurs in spring not in summer and the lowest in the
autumn instead of winter. Although most of the ozone is
generated over tropics but its concentration is maximum
at poles this is because of prevailing stratospheric wind
patterns which distribute the ozone poleward and down-
ward in the l ower st ratosp here. T he value of oz o ne shoul d
be around 260 D. U nea r the equat or so it is a thr esh old for
ozone in the tropics region Figure 7.
3.3.1. Winter
In winters the concentration of ozone remains above
permissible limit, i.e., 260 D.U except in 1993 the value
of ozone reaches near the threshold. The highest value of
ozone in winters can be observed in 1990 which is 292
D.U. (Figure 7(a)).
3.3.2. Spri ng
In spring the concentration of ozone also remains above
the permissible limit of 260 D.U. This shows th ickness in
ozone layer over Pakistan is maximum during the season.
The highest value of ozone in springs can be seen in
1991 i.e., 316 D.U. (Figure 7(b)).
3.3.3. Summer
In summer season is a period of extreme high tempera-
tures. The thickness of ozone is also above the threshold
during summer. The peak value of ozone in summers is
292 D.U in 1990 & 2005 ( Fi gure 7(c) ).
3.3.4. Au tumn
The ozone layer thinning is maximum all over the globe
during autumn. The same situation can be analyzed dur-
ing the autumn season in the atmosphere above Pakistan.
The value of ozone reduced to a large extent and it falls
below the permissible limit of 260 D.U. The lowest value
of ozone in autumn is 242 D.U in 1998 (Figure 7(d)).
The seasonal analysis therefore refers to the highest
amount of total column ozone in spring which falls over
the course of the summer to their lowest amounts in Oc-
tober - November which then further rise again over the
course of winter. The wind transport is the major factor
responsible for the seasonal variations of ozone patterns.
Besides, atmospheric circulation pattern solar intens ity is
also responsible for ozone seasonal variation. Table 1
shows the change in amount of ozone during different
seasons over the last 21 years.
3.5. Ozone & Solar Radiations
The annual and monthly averages of solar radiations are
plotted against the average observed ozone in the strato-
Figure 7. Seasonal analysis of ozone in (a) winter; (b) spring;
(c) summer; (d) autumn over Pakistan 1987-2008.
sphere to verify their interdependence over each other.
This is because solar radiation plays a vital role in sea-
sonal variation of ozone. The solar radiation reaches the
instrument after crossing the ozone layer. Therefore its
value can give us good idea about the status of ozone
measured by Dobson spectrophotometer. The plenty of
Chlorine and Nitrogen compounds are produced in the me-
sosphere and lower thermosphere during h igh solar activity
which are responsible for ozone depletion. Figure 8(a)

Status of Stratospheric Ozone over Pakistan 1987-2008 380
Table 1. Change in total ozone in each season over Pakistan
1987-2008.
Season 1987-2008
Winter - 3.15 D.U
Spring -10.5 D.U
Summer - 6.3 D. U
Autumn - 2.0 D.U
is a graph between annual amount of ozone and solar
radiations evidently depict that when solar radiations are
more intense the ozone thickness shows decrease. Where
as in episodes where solar radiations are less intense the
values of ozone increases. So ozone and solar radiations
are inversely proportional to each other. Figure 8(b)
shows the correlation between the two variables is R2 =
0.44 and statistically significant.
The average monthly values of ozone and solar radia-
tions demonstrate that from January to April when solar
radiations are less intense the ozone thickness reaches to
its high levels. But from May till December due to high
intensity of so lar radiations the ozone concentration starts
decreasing. The increase in solar intensity and decrease
in concentration of ozone over Pakistan have been
clearly illustrated in Figure 9. The correlation between
the two variables, i.e., R2 = 0.35.
(a) (b)
Figure 8. (a) Average annual solar radiations & ozone observed at GC Quetta from1989-2008 and (b) Linear Regression.
Figure 9. Average monthly solar radiations & ozone over Pakistan from 1989-2008.

Status of Stratospheric Ozone over Pakistan 1987-2008 381
3.6. Relation among Ozone, Temperature &
Carbon Dioxide (CO2) Trends
The temperature anomalies have been drawn at different
levels (1000 hPa, 850 hPa, 700 hPa, 500 hPa, 300 hPa,
100 hPa 50 hPa, and 15 hPa). The temperature anomalies
have shown increasing trend in temperatures till 200 hPa
then from 100 hPa to 50 hP a there’s no significan t rise or
decrease has been observed and at 15 hPa decreasing
trend of temperatures have been noticed during the study.
The temperature anomalies at 15 hPa indicate a small
cooling of about −1.3℃ from 1987-2008 in the strato-
sphere Figure 10. This change in temperatures at 15 hPa
will change the rates of chemical reactions which are
involved in the ozone layer production. Several natural
and manmade factors like solar cycle, volcanic eruption,
ENSO, atmospheric nuclear tests, air traffic, spring time
Antarctic ozone hole and an increase in emissions of
Carbon dioxide (CO2) contributes to ozone and tempera-
ture variability.
The ozone depletion leads to less absorption of Ultra
Violet radiations from sun. Therefore the solar radiations
will not convert in to heat radiations and ultimately
cooling will occur in the stratosphere. On the other hand
global warming induced high concentrations of Carbon
dioxide (CO2) have greater warming potential so it emits
heat radiations. The green house gases in troposphere
trap majority of the infra red radiations within tropo-
sphere. Therefore Car bon d ioxid e (CO2) emissions due to
air crafts in the stratosphere will produce heat which will
be larger than the energy received from troposphere
hence the net energy loss results in cooling. The graph of
average annual carbon dioxide and ozone shows reduc-
tion in total ozone and sharp increase in carbon dioxide
emissions during a study period over Pakistan. Further
Figure 11(a) clearly illustrates that with the increase in
CO2 emissions in the last decade the total column ozone
over Pakistan has decreased. Hence reduced ozone
causes the stratosphere to absorb less solar radiation, thus
cooling the stratosphere while warming the troposphere.
The maximum concentration of ozone appears in
spring and summer and minimum concentration during
winter and very less concentration during autumn. There-
fore it is presumed that during spring and summer the
most of the carbon dioxide is consumed by the vegetation
in photosynthetic activity so less amount of carbon diox-
ide got a chance to escape in to the atmosphere. So the
concentration of ozone does not disturb much during
summer and spring. Comparatively in autumn and winter
there is less vegetation, so less consumption by the trees
and more emission of carbon dioxide in the atmosphere.
In autumn when ozone concentration falls below thresh-
olds more ultra violet radiations reaches the earth making
troposphere warmer.
The carbon dioxide and ozone are inversely propor-
tional to each other means that when ozone remains
maximum the carbon dioxide emissions will be less and
vise versa. The correlation between the average annual
ozone and carbon dioxide is R2 = 0.3 which is statisti-
cally significant at 95%confidence level Figure 11(b).
Figure 10. Average temperature anomalies at 15 hPa over Pakistan from 1987-2008.

Status of Stratospheric Ozone over Pakistan 1987-2008 382
(a) (b)
Figure 11. (a) Average annual carbon dioxide (CO2) emissions and ozone (O3) of Pakistan from 1987-2007; (b) Linear regres-
sion.
4. Conclusions
The annual, monthly and seasonal analysis of strato-
spheric ozone data has been done during the study (1987-
2008). All the analysis have shown decreasing trend of
stratospheric ozone supporting the evidence of ozone
layer depletion over Pakistan. The change in annual
depth of total column ozone is −5.67 D.U. The total de-
crease found during monthly analysis is −4.2 D.U. The
maximum value of ozone is observed in spring (> 260
D.U) while the lowest value of ozone is observed in au-
tumn (< 260 D.U). The total change calculated in spring
is −10.5 D.U, summer is −6.3 D.U, winter is −3.15 D.U
and autumn is −2.0 D.U. The Japanese Reanalysis data
also used to monitor ozone layer thickness therefore a
comparison between observed and predicted values have
been made to confirm the ozone layer is thinning over
Pakistan region. Both the data sets have portrayed a cor-
relation coefficient of 0.6. The average ozone has been
plotted against average solar radiations for both annual
and monthly analysis to figure out the mutual interde-
pendence of the parameters. It is concluded that ozone
and solar radiations are inversely proportional to each
other. The correlation coefficient for the variables on
annual basis is 0.44 and on monthly basis is 0.35. From
December to April when solar radiations are less intense
the ozone thickness reaches to its peak values. Whereas
from May till November due to high intensity of solar
radiations the concentration of ozone minimize and its
concentration during October and November reduced so
much that ozone reaches to its threshold values over
Pakistan. The trend of small cooling has been seen in the
stratosphere and the total change in temperature of
stratosphere is about −1.3℃ from 1987-2008. The reason
for lower temperatures of stratosphere has been related
with increased carbon dioxide (CO2) emissions in the
atmosphere. The correlation between ozone and carbon
dioxide emissions is R2 = 0.3 which is statistically sig-
nificant at 95% confidence level. The graph between
ozone and carbon dioxide shows that with increasing
concentration of carbon dioxide is not only contributing
to global warming but also play role in ozone layer de-
pletion.
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