Indian J. Phys. Vol. 85, No. 8, pp 1247-1256, August, 2011
Seasonal variation of daily total column ozone (TCO) and role of its depletion and formation rate on surface temperature over Dumdum at Kolkata, India S K Midya1,2*, D Ghosh3, S C Ganda1 and H Sarkar1,4 1
Department of Atmospheric Sciences, University of Calcutta, 51/2, Hazra Road, Kolkata-700 019, India 2
Indian Centre for Space Physics, 43 Chalantika, Garia Station Road, Kolkata-700 084, India 3
Department of Chemical Engineering, Jadavpur University, Kolkata–700 032, India
4
Centre for Microwave and Millimeter Wave Research and Training, Institute of Radio-Physics and Electronics, University of Calcutta, 92 A.P.C. Road, Kolkata-700 009, India E-mail :
[email protected]
Received 08 April 2010 accepted 28 November 2010
Abstract : The purpose of the paper is to present the variation of total ozone concentration over Dumdum at Kolkata, India during different seasons. It is concluded that the trend of ozone concentration during different seasons are different. A critical analysis is done and following important results are obtained. (i)
The total ozone concentration increases during the pre-monsoon and winter periods. During premonsoon period rate of formation of ozone increases sharply with the rise of surface temperature.
(ii)
TCO decreases during the monsoon and post-monsoon periods, throughout the period of study. During monsoon period rate of depletion of ozone increases and during post-monsoon period rate of depletion of ozone decreases with the increase of temperature.
(iii)
Possible explanations are also presented.
Keywords : Stratosphere, Troposphere,TCO PACS Nos. : 94.10.Fa, 94.10Rk
1. Introduction Ozone is mainly found in two regions of the Earth’s atmosphere. Most ozone (about 90%) resides in a layer between approximately 10 and 50 km above the surface of Earth, the region of the atmosphere called the stratosphere. The remaining ozone is in the lower *
Corresponding Author
© 2011 IACS
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region of the atmosphere and it is called the troposphere. The total column ozone indicates both the tropospheric as well as stratospheric ozone over a specified region. Ozone studies over India and other regions have already been done by different investigators [1-8]. In a previous communication it is reported that the trend of ozone concentration over Dumdum at Kolkata, India is decreasing [9].This paper presents variation of the rate of change of ozone concentration over Dumdum in different seasons during the period 1996 to 2004 and possible explanations are also presented.
Figure 1. Daily variation of ozone during Winter showing increasing trend during the whole period of study.
Seasonal variation of daily total column ozone (TCO) and role of its depletion and formation etc
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2. Method and analysis Ozone data of Dumdum for the period 1996-2004 are taken from internet website http:// jwocky.gsfc.nasa.gov and surface parameter data are taken from www.weather.uwyo.edu The collected data were divided into the following four parts – z
Pre-monsoon period – the months of March, April, May and upto 7th June
z
Monsoon period – the months of June (8th onwards), July, August, September and October (up to 10th).
z
Post-Monsoon period – the months of October (11th) onwards, November & December.
z
Winter period – the months of January and February.
3. Results and discussion 3.1. Daily variation of ozone: Total ozone concentration is plotted against days, in a scatter diagram, for the different time periods as mentioned above. The trends that were observed in the different time periods are given below: The trend during winter (Fig. 1) and Pre-monsoon (Fig. 2) clearly shows an increasing tendency, i.e. the total column ozone concentration increases throughout the period of study. However, the reverse trend is observed for Monsoon (Fig. 3) and Post-monsoon (Fig. 4). 3.2. Rate of change of TCO during different seasons : The schematic representations of the variation of rate of change of the daily changes in the total ozone from 1996 to 2004 are presented in Table 1. Non-availability of data is indicated by 0 in the Table. The general trend clearly shows a positive gradient value in the pre-monsoon and winter periods and negative values in the monsoon and post monsoon periods. In other words it can be said that there is an increase in the ozone concentration during the months from October to February (i.e. post monsoon and winter) and a decrease in the same from March to May and upto 8th June (i.e. Pre-monsoon and monsoon).Within the period of study, in the pre-monsoon period, a maximum positive value of the rate of change of TCO is shown in the year 1999. However in the winter period the same is observed in the year 2000. The magnitude of the positive gradients is much greater during the pre-monsoon period than in winter. Both in monsoon and post-monsoon period, negative gradient values are observed, with more negative values in the post-monsoon period as compared to the monsoon period. The highest negative value in monsoon is found in the year 2003 and that in the post-monsoon period in the year 1996.
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Figure 2. Daily variation of ozone during Pre-monsoon showing increasing trend during the whole period of study.
Seasonal variation of daily total column ozone (TCO) and role of its depletion and formation etc
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Figure 3. Daily variation of ozone during Monsoon showing decreasing trend during the whole period of study.
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S K Midya, D Ghosh, S C Ganda and H Sarkar
Figure 4. Daily variation of ozone during Post-monsoon showing decreasing trend during the whole period of study.
Seasonal variation of daily total column ozone (TCO) and role of its depletion and formation etc
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3.3. Variation of depletion and formation rate of O3 concentration with surface temperature : The variation of formation and depletion of O3 concentration with surface temperature over Dumdum at Kolkata, India during different seasons are shown in Fig. 5-7. It is clear from Fig. 5 that premonsoon rate of formation of ozone increases with the rise of surface temperature. During monsoon period rate of depletion of ozone increases with the increase of surface temperature (Fig. 6). During post-monsoon period rate of depletion of ozone decreases with the increase of surface temperature (Fig. 7).
RATE OF CHANGE OF TCO
PRE-MONSOON
y = 0.125 x – 3.4455 R2 = 0.7237
0.6 0.4 0.2 0 29.5
30
30.5
31
MEAN SURFACE TEMPERATURE
Figure 5. Variation of rate of change of TCO with mean surface temperature (0C) during Pre-monsoon period.
In a previous communication [10], it is shown that average O3 concentration is declining over Dumdum with smaller amount. This paper confirms that during pre-monsoon and winter period O3 trend is positive and rate of change of O3 concentration is highly correlated with surface temperature. During other seasons depletion rate of O3 predominates and overall O3 concentration shows slight depleting trend. The average trend of O3 concentration over Dumdum for the period 1996-2004 is shown in Fig. 8. It is clear that overall O3 concentration over Dumdum for the period our study shows slightly increasing trend. Different formation and destruction processes of ozone are given below: MONSOON RATE OF CHANGE OF TCO
0 –0.05
28.9
29
29.1
29.2
29.3
29.4
–0.1 –0.15
y = – 0.3798x + 10.962 R2 = 0.8225
–0.2 SURFACE TEMPERATURE (0C)
Figure 6. Variation of rate of change of TCO with mean surface temperature (0C) during Monsoon period.
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S K Midya, D Ghosh, S C Ganda and H Sarkar
Reactions
Rate Constants
1.
O3 + hv
abs o
O3*
Iabs
2.
O3*
K1 o
O2 + O
K1
3.
O + O3
K2 o
2O2
K2
4.
O + O*3
3 o
2O2
K3
5.
O+O
K4 o
O2
K4
6.
O + O2
5 o
O3
K5
I
K
K
Midya et al [11] established an empirical equation of O3 concentration with the concentrations of other atmospheric constituents. [O3]= {K5[O2]/K2}-{Iabs/K2[O]} – {1/K2[O]} exp [–K2[O](K10 + t)] [O3], [O2] and [O] are the concentrations of ozone, molecular oxygen and atomic oxygen respectively. Iabs and all K values are the rate constants of different reactions and these values can be determined from chemical kinetics [11]. The net reaction for the formation of ozone in stratosphere is given below : O2 + O2 o O2 + O + O = O3 + O O + O2 + M = O3 + M 3O2 = 2O3 Ozone formation reaction is endothermic. So higher temperature will favour higher equilibrium concentration of O3. Again if temperature decreases rate of formation of O3 will also decrease. Thus it is quite expected that concentration decreases with the decrease of temperature. During pre-monsoon period, temperature of surface is higher. So in order to obtain higher concentration of ozone, rate of formation of ozone will be higher during
RATE OF CHANGE OF TCO
POST -MONSOON 0 23.8
24
24.2
24.4
24.6
24.8
–0.2
–0.4
y = – 0.0896x4 + 6.415x3 – 151.61x2 + 1147x + 845.86 R2 = 0.5227
–0.6 MEAN SURFACE TEMPERATURE
Figure 7. Variation of rate of change of TCO with mean surface temperature (0C) during Post-monsoon period.
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pre-monsoon period and will increase with the increase of surface temperature. So the nature of variation as shown in Fig. 6 is quite expected. Depletion mechanism of O3 as given by Bates and Nicolet [12] is given below: OH + O3 o HO2 + O2 HO2 +O o OH + O2 _________________ O3 + O o 2O2 Again atomic and molecular oxygen are produced due to the decomposition of H2O molecule in the troposphere. This is done by unabsorbed solar UV ray as given below [8]. H2O o H + OH OH o O + H O + O + M o O2 + M During monsoon period probability of OH increases in the atmosphere. As a result depletion rate increases with the rise of temperature as probability of H2O molecules in vapour state increases with the rise of temperature which is observed in Fig. 7. During post-monsoon period probability of H2O molecules in vapour state decreases and as a result depleting rate of ozone gradually decreases Fig. 7 during post-monsoon period [11].
OZONE CONCENTRATION (D.U.)
400
Y = 0.0014X + 267.12
350 300 250 200 150 100 50 0 0
500
1000
1500
2000
2500
3000
DAYS (0 STANDS FOR JANUARY 1, 1997)
Figure 8. Variation of ozone trend over Dumdum for the period of 1996-2004.
4. Conclusion It is concluded that the rate of change total ozone concentration over Dumdum at Kolkata, India are not same for all seasons. It depends on the change of surface temperature for different seasons. It is also concluded that ozone concentration over Dumdum shows slight increasing trend for the period of study. This type of variation is explained considering ozone destruction mechanism which was given by Bates and Nicolet [12].
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