© 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved.
Web: www.witpress.com Email [email protected]
Paper from: Air Pollution X , CA Brebbia & JF Martin-Duque (Editors).
ISBN 1-85312-916-X
Diurnal variation of air pollution concentration
during winter in Kathmandu valley
M. L. Shresthal, A. Kagal, A. Kondol, Y. Inouel &B. Sapkota2
‘Department of Environmental Engineering, Osaka University, Japan
21nstitute of Engineering, Pulchok Tibhuvan University, Nepal
Abstract
The air pollution concentration during the winter season in Kathmandu valley is
high compare to the summer season. NOZ concentration and TSP concentration
measurements were done on the roof of the Institute of Engineering, Tribhuvan
University, ‘Nepal h, February 2001. Simultaneously, temperature was measured
at Raniban Mountain located in the north east of Kathmandu city at the height of
60m, 220m and 400m above the Institute of Engineerkg.
The air pollution
concentration of Kathmandu valley was seen to increase gradually after sunset
and increased abruptly from early morning and reached the maximum value from
6 am to 9 am. After that, it showed an abrupt decrease and became the minimum
value in the daytime. From nighttime till early morning, the temperature at the
lower height (60m) was seen to be lower than the te~perature at the higher
height (400 m). It shows that strong inversion layer is formed in Kathmandu
valley and the air pollution concentration in the valley is strongly influenced by
the inversion layer.
© 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved.
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Paper from: Air Pollution X , CA Brebbia & JF Martin-Duque (Editors).
ISBN 1-85312-916-X
654
1
Air pollution x
Introduction
Kathmandu is an architectural valley surrounded by mountains and possesses
marvelous scenery of Himalayas at the northern side of valley. It is located at the
center portion of the east west running Himalayan belt and has flat lands that
stands at an elevation of about 1300 m to 1400 m above sea level. It is the largest
urbanized area with a population of about 450,000 and covers an area of about
600 kmz. With the geographic structure of Kathmandu, air pollution has become
one of the most major concerns.
As air is the major concern, many researchers ‘1’2]
have focused the environmental
problems in the capital of Nepal- Kathmandu. The environmental status of
Kathmandu is getting worse. The growing population density, increasing number
of vehicles, dusty roads and industries are considered to be the main causes of
the increasing tendency of pollution. The increasing number of air related
diseases demands a lot of medical expenses. The pollutants have also been the
main cause M the decreasing tendency of the visibility distance in the valley,
which have hampered the scenery of the Himalayas resulting in the adverse
effects to the tourism industry.,
Kathmandu valley is considered the most polluted city among the other cities of
Nepal. The pollutants measured in the valley in the past researchers show the
high concentration during the winter. In this paper, diurnal pollutants were
measured k the valJey from the end of February till the beginning of March.
Diurnal measurement of the ambient air pollution concentration and potential
temperature gives the clue of the mechanism of the air pollution of Kathmandu
valley.
2 Measurement
items, place and period
The measurements were undertaken in the following condition shown in table 1.
© 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved.
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Paper from: Air Pollution X , CA Brebbia & JF Martin-Duque (Editors).
ISBN 1-85312-916-X
Air Pollution X
655
Table 1: Measurement items, places and period
Contents
Place
Temperature
TSP
N02 & S02
Mt. Raniban
Institute of Engineering, T. U.
Period
2/22-3/08
2/22-3/11
Altitude
1320m
1380m
(above sea
(lOm from ground height)
1540m
level)
Method
1720m
Sampling of
Digital Dust
Thermometer
TEA filter
Monitor
Chino
Shibata Inc.
Inc.(MR5300)
(LD-3)
I
Interval
3 Hour
10 min
1 minute
2.1 Measurement method
2.1.1 Temperature
Raniban Mountain located at the north east of Kathmandu valley, was used as
the station for the measurement. The l’t, 2ndand 3rdthermometers were placed
at the altitude of 1380m, 1540m and 1720m from the sea level respectively so
that these thermometers were 60m, 200m and 400m above respectively from
the Institute of Engirieering campus, Tribhuvan University. The measurements
were done at the interval of 10 minute.
2.1.2 N02 and S02
NOZ and SOZmeasurements were done by using a sampling equipment shown in
fig. 1. Time set of the timers was shown in table 2.
Table 2:
Table of time set
Timer No.
1
2
3
4
5
6
7
8
Time Set
o-
3-
6-
9-
12-
15-
18-
21-
3
6
9
15
18
21
24
(Hour)
12
© 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved.
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Solenoid valve
Filter Hol
Timer
Air IN
I
-
‘ Electric Power Supply
Pump
Air OUT
Figure 1. The schematic flow diagram of NOZand SOZsampling system
This equipment was developed in Osaka University in order to sample NOZ and
SOZin the atmosphere. The equipment was constructed in such a way that 8 sets
of filter holders were used in a day by changing the filter holders automatically
one by one after every 3 hours of sampling.
This equipment consists of filter holders, solenoid valves, timers, and a pump. A
set of filters in a filter holder consists of 5 sets of TEA (Tetraethanol Amine
Acetone) absorbed filters (120mm x 120mm ) for the absorption of NOZand SOZ
and a sheet of glass filter @ air contact outer side to prevent the dust. Eight sets
of filter holders, valves and timers were used as shown iq fig. 1. Each valve was
controlled by a timer with 3 hours of time difference so that just one valve is
opened at a time, The air was sucked by the pump continuously and filters were
changed everyday. The measurements of N02 and SOZabsorbed were done by
Photo Spectrometer and Ion Chromatography, respectively.
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2.1.3 TSP
The measurement of TSP was performed at the same place (Tribhuvan Univ.)
where the measurement of N02 and S02 were undertaken. Digital dust monitor
was used for the measurements and the measurement interval was 1 minute.
3 Results
3.1 Temperature
Fig. 2 shows the result of the temperature measurement at the height of 60m,
220m and 400m above the ground level of Tribhuvan University.
I
Month/Day
Figure 2. Temperature measurement at 60m, 220m and 400m above Kathmandu
valley
At daytime, the temperature at the lower altitude was higher than the temperature
of higher altitude but as the nighttime approached, the temperature at the lower
altitude (60m) became lower than the temperature at the higher altitude (220m
and 400m) which shows the opposite pattern from the day temperature. This
phenomenon was shown in both the temperature comparison between 60m and
400m as well as 60m and 220m. This evidence proves that an inversion layer
was formed during the night.
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3.2 NOZ and SOZ
Fig, 3 shows the N02 concentration variation of Kathmandu valley. Everyday,
peak of concentration was realized.
25.00
20.00
~ 15.00
A
~ 10.00
z
5.00
0.00
Figure 3. N02 measurement
Fig. 4 shows the diurnal variation of NOZ.The highest concentration of NOZwas
found everyday in the morning between 6 am to 9 am. After which, the
concentration of N02 gradually decreased and again, the second peak was found
between 6 am to 9 am.
~22-Feb
---++--
23-Feb
--I&--.2
,;,:.
Febeb
25-Feb
-26-Feb
-4--27
-Feb
-28-Fab
—1
-M.,
. . ..k. . . ..~. ~ar
3- M.,
4- M.,
..+--..5-Mar
..,,:. ...8-).4..
I
Time [Hr.]
. ..+.....7-M..
Figure 4. Diurnal NOZ concentration variation of Kathmandu valley
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Fig. 5 shows the concentration of SOZbut it does not show the daily peak as NOZ
data.
60
,,,4+
50
~
40
I
~22-Feb
—23-Feb
::$,
‘---&
-.2 4-F.
:.,:
N
CJ
b
25-Feb
-X-26-Feb
20
—27-Feb
Ma,
—1....... ... . -Mar
10
o
Figure 5. Diurnal SOZconcentration variation of Kathmandu valley
3.3 TSP
Fig.6 shows the daily TSP variation of Kathmandu valley.
manner as N02, TSP also shows the daily peak.
400
350
300
‘7
E 250
~ 200
r 150
: 100
50
0
Month/Day
Figure 6. TSP Measurement
In the similar
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Fig. 7 is the graph of the 3 hr. average TSP data. This result also shows the
peak of TSP everyday from 6 am to 9 am. Then, TSP concentration gradually
decreased to 3 pm and again increased slowly.
~22-Feb
300
,:::,,
1
1
~23-Feb
-------
24-Feb
,.:25-Feb
—26-Feb
--+--
27-Feb
—28-Feb
—1
-M.,
. . . .......2-M..
3- M,,
4- M.,
--+----
5-M.
r
:,:6-M.,
....+7-M.,
Time [Hr.]
. . . ..!...8-).4..
L___
Figure 7, Diurnal TSP variation of Kathmandu valley
3.4 Correlation between TSP and N02
Fig. 8 shows the correlation between TSP and NOZ concentration. The graph
shows that TSP is directly proportional to N02 concentration.
300
250
F/
E 200
~
150
& 100
150
0
o
5
15
10
20
N02 ~pb]
Figure 8. Correlation between TSP and NOZ
25
© 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved.
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3.5 Vertical potential temperature and TSP
The vertical axis of fig. 9 was the potential temperature, which was drawn by
calculating the temperature difference between 60m and 400m above the
Kathmandu valley (Engineering campus). The potential temperature in fig. 9 and
TSP concentration in fig.6 were compared. The portion above the zero line in
fig.9 is the stable condition of the atmosphere but the portion lower than zero
level is the unstable atmosphere. When the atmospheric condition become stable,
concentration of TSP had a tendency to become high.
Figure 9. Vertical Potential temperature
4 Conclusions
It is quite clear from the above results that diurnal atmospheric polhrtion of
Kathmandu valley possesses a cyclic change. The concentration of NOZ, TSP
value becomes highest during the morning from 6 am to 9 am. The main reason
of the hig Kpollution concentration during that time is considered due to the not
complete destructiori of the inversion layer formed at the nighttime. The layer of
the pollutants is deposited between the heights of 60inl and 400m above the
Kathmandu valley. The inversion layer induced the high pollutant concentration.
The layer of the inversion layer formed at nighttime and vehicles cause the high
concentration of TSP and N02 at the morning hour. The sun ray destroys
inversion layer which results the low concentration of TSP and NOZ at day time.
NOZ and TSP increases again from evening as inversion layer is formed again..
© 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved.
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Paper from: Air Pollution X , CA Brebbia & JF Martin-Duque (Editors).
ISBN 1-85312-916-X
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Air pollution X
References
[1] Urban air quality management strategy in Asia (URBAIR), Kathamndu
valley report, October 1996,The World Bank
[2] Urban air quality management strategy in Asia, Kathmandu valley report,
World Bank Technical Paper No. 378.