This document analyzes air pollution climatology data from Bhopal and Gwalior, India over a 5-year period. It finds that April has the highest mixing height and ventilation, suggesting best pollutant dispersion. January and October are worst for vertical dispersion. Daytime generally allows for better dispersion than nighttime. Bhopal experiences more unstable conditions and better dispersion than Gwalior. Industries should be located south of cities to minimize pollutant effects, as prevailing winds are from the north.

1. Indian Journal of Air Pollution Control Vol. V No. II September 2005 pp 24-33
Air Pollution Climatology Of Bhopal And Gwalior
Anish Chandra Pandey*, B.P. Murty** and R.R. Das***
*Department of PG Studies and Research in Chemistry, Govt. SLP PG College,
Morar (Jiwaji University), Gwalior – 474006 (MP); E-mail Id: dracpandey@yahoo.co.in
**Professor in Meteorology, School of Environmental Sciences, JNU, New Delhi - 110067
*** Former vice chancellor, Jiwaji University, Gwalior and Shri RS International University, Raipur
Abstract
The present study aims at seasonal and diurnal pollution potential around Bhopal, the capital region of Madhya Pradesh and
Gwalior. For this purpose, meteorological data of two stations, viz. Bhopal and Gwalior for five years (1994-1998) have
been analyzed. Four seasonal representative months, viz. winter (January), pre-monsoon (April), Monsoon (July) and post-
monsoon (October) have been selected for detailed studies. Analysis shows absence of stable conditions in the daytime and
unstable condition in the night in each month. April shows the highest mixing height and ventilation coefficient. Results
seem to suggest that daytime is suitable for good dispersion in all the months, pollutants are well dispersed in April and
July, and January and October are the worst months for vertical dispersion of pollutants / contaminants. As the predominant
winds are northerly, any industrial set up should be in the leeward side i.e. in the south of the city in order to minimize the
effect of pollutants.
Key Words: Meteorological Parameters, Pollution Potential, Wind Roses, Stability, Inversion,Ventilation Co-efficient.
Introduction
Bhopal (latitude 230
27/
N, longitude 770
43/
E and altitude above 503m m.s.l.), the capital town of Madhya
Pradesh situated on the eastern edge of Malwa plateau and located in the central part of the state with tropic of
cancer passing through it, is facing severe environmental pollution problems. Gwalior, the third largest city of
Madhya Pradesh is situated in the northern part of MP and lies between latitudes 250
34/
N and 260
21/
N, and
longitudes 770
40/
E and 780
54/
E and has altitude 207m above m.s.l. The city sprawls over the horseshoe
shaped valley surrounded on three sides by low Vindhyan hills in the west and Bijawar hills in the southeast. The
space between these two is filled with residual hills viz., Hanuman hill, Gupteshwar hill, Satyanarayan hill, and
Fort hill, providing an aesthetic frame to the city urban form.
Air pollution climatology explains the ability of the atmosphere to dilute or stagnate pollutants over a
region at any time, since the pollution levels at any place and time represent a balance between the rates of
emission from their sources and the rate at which they are removed from the atmosphere (Wark and Warner,
1976). For a particular region thus temporal variations of pollution depend upon the rate of emissions and the
existing meteorological conditions. The parameters involved in this type of study are thus the temporal and
spatial variations of wind, stability conditions, inversion depth, mixing height, and ventilation coefficient etc.
The present study aims to examine the role of climatological factors in the dispersal or diffusion of air
pollutants released into the atmosphere of Bhopal and Gwalior.
Materials and Methods
Meteorological data of Bhopal and Gwalior for four representative months corresponding to seasons viz. Winter
(January), Pre monsoon (April), Monsoon (July) and Post monsoon (October) for five years period (1993-1997)
have been used. Daily radiosonde data of two stations viz. Bhopal and Gwalior for the period 1985-89 (Jan, Apr,
July, Oct) from surface to 700 mb at 00 GMT, has been analysed to get information about the upper air wind
roses, inversion depths, mixing heights and ventilation coefficients.

2. Results and Discussion
Study of Winds
Seasonal wind roses for Bhopal and Gwalior are presented in Fig. 1 and Fig. 2. It may be seen that the
frequencies of occurrence of calm periods are higher at Gwalior than at Bhopal for all the representative months.
Out of the four representative months, the highest calm periods at Gwalior are 88% in January and 96% in
October and at Bhopal the highest (57%) calm period is in October. Since, the calm/weak winds increase the
concentration of pollutants at ground level whereas strong winds carry the pollutants far away from the source
and dilute them (Munn, 1970 and 1976), it can be inferred that the occurrence of calm winds in the evening can
accumulate and stagnate the pollutants leading to increased ground level concentrations deteriorating air
quality. For the same reason, poor carrying capacity of the atmosphere is expected in winter followed by post-
monsoon season whereas better carrying capacity is expected in summer followed by monsoon season when
strong winds blow. Out of the two cities under our consideration, better dilution of the pollutants leading to
reduction in ground level concentration is expected at Bhopal compared to Gwalior due to prevalence of stronger
winds there. Further, since the predominant winds are in the N, NE and WSW in both the cities, so it is
suggested that any new industrial set up should be in the down wind of the city (i.e. South /South West of the
city) in order to minimize the effects of pollutants.
Figure 1: Seasonal wind roses for Bhopal

3. Figure 2: Seasonal wind roses for Gwalior
Study of Stabilities
Pasquill stability classes were determined by the use of Turner's (1964) and Holzworth (1974) methods for
Bhopal and Gwalior. This atmospheric stability classification is based on latitude, cloudiness and wind speed. In
this classification extreme instability is associated with maximum dispersion of pollutants. Inhibition of
turbulence associated with inversions and calm periods leads to stable atmosphere causing minimum diffusion of
pollutants i.e., stagnation of pollutants. Neutral atmosphere is the intermediate stage between these two that may
move towards instability on one side and stability on the other.
The frequencies of occurrence of all stability classes are given in Table 1 for Bhopal and Table 2 for
Gwalior for both day and night periods separately.
Table 1: Pasquill Stabilities at Bhopal (Turner, 1964)
Month Percentage Frequency
Day Night
A B C D D E F G
January 19.3 4.7 15.1 12.8 0.9 1.6 7.9 37.7
April 5.7 15.9 14.3 13.7 4.5 7.4 12.6 25.9
July 0.9 7.9 8.0 32.9 12.4 9.0 21.5 7.4
October 11.5 6.8 15.0 16.9 2.6 1.3 10.1 35.8

4. Table 2:Pasquill Stabilities at Gwalior (Turner, 1964)
Month
Percentage Frequency
Day Night
A B C D D E F G
January 9.7 18.0 17.4 5.3 1.9 0.7 10.1 36.1
April 10.3 14.2 12.1 14.1 2.8 3.8 12.0 31.9
July 0.8 4.7 17.7 27.0 21.3 4.7 20.9 3.1
October 10.5 16.9 14.5 9.3 5.7 0.9 12.4 32.0
A-Extremely unstable, B-Moderately unstable, C-Slightly unstable, D-Neutral,
E-Slightly stable, F-Moderately stable, G-Extremely stable
It may be seen from the above Tables that no unstable conditions have been observed during nighttime
and no stable conditions have been reported during day time at either of the stations in all the four representative
months of the season. These results are in good agreement with that of Hosler (1961), Sadhuram and Vittalmurty
(1986) and Padmanabhamurty and Tangirala (1988). The neutral stability "D" has occurred both during day and
night but its frequency was less during night for both the stations in all the months. Thus, there are four classes -
Extremely unstable (A), Moderately unstable (B), Slightly unstable(C) and Neutral (D) for day time and four
classes - Neutral (D), Slightly stable (E), Moderately stable (F) and Extremely stable (G) for nighttime.
Frequencies of stability classes "F" and "G" have higher values than "D" and "E" at both the stations in the
nighttime except in July in which "D" has the highest value for Gwalior. Except in the month of April (i.e.,
Summer), Bhopal experiences more frequencies of "G" stability than Gwalior. Thus, it can be concluded form
the present study that dispersion capacity at Bhopal is higher than at Gwalior because of comparatively more
unstable conditions at Bhopal. Better dispersal of pollutants during the day time can be expected especially in
summer (April) and monsoon (July), whereas, poor dispersion is expected at night particularly in winter
(January) and post monsoon (October).
It has been observed that inversion and stable conditions occur more frequently in the morning hours and
less frequently in the evening hours in all the representative seasonal months for both the stations. Due to the
increase of solar radiation and air temperature, the stable condition of the atmosphere in the morning time
change into unstable condition in daytime, which increases the turbulence in the atmosphere. The case is vice-
versa for the evening and nighttimes. According to Ogawa et al. (1985), the turbulence intensity decreases as the
stability of the atmosphere changes from unstable to stable condition. Based on these considerations it may be
concluded that turbulence intensity in the daytime is expected to decrease slowly in January (Winter) and rapidly
in July (Monsoon) followed by April (Pre-monsoon). It is generally observed that no definite direction is
associated with any stability; however winds are comparatively stronger during unstable conditions. From these
studies, it can therefore be concluded that better diffusion conditions exist in April and July and also during
daytime in all the months under both unstable and neutral conditions.
Studies of Inversions
Inversions may be ground based or elevated. Ground based inversions are formed due to radiation emission from
the ground during evening and nighttime. The development of elevated inversions takes place from large-scale
subsidence of air masses that stagnate and then sink over the area. According to Milan et al., (1988) large-scale
subsidence is associated with warming and inversion development. Elevated inversions are also advected.
Kallos et al., (1993) has observed that advection inversions are usually deeper and in several cases do not even
dissipate during the day hours, especially during winter and transient seasons. Elevated inversions are not easily
dissipated and can persist for longer periods.

5. Percentage frequencies of ground based inversions with various top heights have been computed for
both Bhopal and Gwalior at 00 and 12 GMT and are given in Table 3. The atmosphere within the planetary
boundary layer (1.5 km) has been considered for this study. The frequencies have been rounded to the nearest
whole number. It may be seen that frequencies of inversions over Bhopal and Gwalior show large variations in
the morning hours and less in the evening hours. Further, the ground based inversions at Bhopal at 00 GMT were
generally restricted to 0900 – 1000 m, while at 12 GMT they never exceeded 501-600m. At Gwalior, however,
ground based inversions extended up to 1401- 1500m at 00GMT, but were restricted again to 501- 600m at 12
GMT. Overall, the frequency of occurrence is more at Gwalior than at Bhopal. This may be due to the complex
topography of Gwalior (rocky and surrounded by hills forming a bowl).
Table 3: Percentage Frequencies of Ground Inversions at Bhopal and Gwalior
STATION TIME (GMT) SEASONAL MONTHS
JANUARY APRIL JULY OCTOBER
BHOPAL 00 GMT 68 49 07 42
12 GMT 07 06 03 05
GWALIOR 00 GMT 81 62 16 53
12 GMT 09 05 02 06
At 00GMT the highest frequencies of inversions have been observed at Bhopal in the month of January
(68%) followed by April (49%), while the month of July (7%) showed extremely low frequency with an increase
again in October (42%). At 00 GMT, the highest frequencies of inversion layers have been shown at Gwalior in
the month of January (81%) followed by April (59%) whereas extremely low frequency was found in the month
of July (16%). It showed increasing trend again in the month of October (53%). At 12 GMT, frequency of
inversions found at Bhopal was 7% in January, 6% in April, 3% in July and 05% in October, whereas at 12 GMT
the frequency of inversions at Gwalior was 9% in January, 5% in April, 2% in July and 6% in October. It has
been reported by Katsoulis (1988a) that these inversions develop frequently during nighttime (for almost half of
the night), and rapidly erode during the day. In July, the minimum frequency of inversions is due to cloudy
weather and strong winds.
Ground based inversions restrict the dispersion of pollutants vertically within it. The top of the inversion
acts as a lid and restricts effectively the dispersal of pollutants released below it and the inversions are thus
responsible to affect the ambient air quality. Considering the role of inversions as above, it can therefore be
concluded that among all the months, January (Winter) may be the worst month for mixing of pollutants,
whereas July (Monsoon) is a better month for dispersion in the study area. This observation is in conformity with
the observation made by Rai and Padmanabhamurty (1993) for Patna. A comparative study of the inversions at
Bhopal and Gwalior shows that better mixing of pollutants is expected at Bhopal than at Gwalior.
Studies of Mixing Height
Hourly mean mixing heights during the day period have been calculated as per Holzworth's (1967) method for
the five years (1985 to 1989) at Bhopal and Gwalior for all representative months of the seasons i.e., January,
April, July and October reveals that:
In January, at Bhopal the minimum mixing height (mean) of 254 meters was observed at 00GMT and
maximum mixing height (mean) of 1444 meters was observed at 09 GMT, where as at Gwalior, the minimum
mixing height (mean) was found at 198 meters at 00GMT and maximum mixing height (mean) was observed at
1389 meters at 09GMT. In April, at Bhopal the minimum mixing height (mean) at 00GMT was calculated as 307

6. meters and mean maximum mixing height (mean) was calculated at 2110 meters, while the respective values at
09GMT for Gwalior were 316 meters and 2099 meters. Similarly for July at Bhopal, the mean mixing heights,
both minimum and maximum respectively, were at 300 meters and 1197 meters, whereas at Gwalior these values
were respectively 207 and 1205 meters. In October at Bhopal, the mean mixing heights, both minimum and
maximum, were found at 225 meters and 1739 meters respectively, while at Gwalior these values were
calculated as 235 meters and 1688 meters. Overall, mixing height is more at Bhopal than at Gwalior.
The difference between maximum and minimum mixing heights during the July month as reported
above is found to be the least in comparison to the other months. This least variation in mixing height in July at
both the stations can be accounted to the overcast conditions which cause lower mixing during the day because
of the relatively low surface temperature but greater mixing at night because of the relatively high surface
temperature. Both at Bhopal and Gwalior, the minimum mixing height has been observed at 00GMT, while the
maximum mixing height has been observed mostly at 09 GMT except in July wherein it has been observed at 12
GMT. The mixing height increases from 00 GMT to 12 GMT and thereafter it decreases. This was due to the
diurnal variation of surface temperature. In all cases, values were minimum during the early morning hours and
maximum during the afternoon. As calm or light winds prevail during nights resulting in greater loss of ground
radiation and no heat source, the nighttime mixing heights are lower compared to the afternoon mixing heights.
Among the four seasonal representative months, the highest mixing height occurred in April followed by
October, January and July. In April, the highest mixing height values may be due to the maximum surface
heating. The percentage frequencies of occurrence of low mixing heights were the maximum in winter due to the
presence of surface based inversions. The highest mixing heights observed during summer (in April) may be due
to the fact that the amount of incoming solar radiation is higher during this season and as the soil is dry, this
radiation is preferably converted into sensible rather than latent heat flux and turbulence, favouring the
development of a deep mixing layer. Contrary to this, the amount of incoming solar radiation is less during
winter and as the soil is moist and covered with vegetation, most of this radiation is converted into latent heat;
thus the vertical development of the mixing layer is reduced. The observed mixing height in the afternoon is
deeper due to the fact that the soil is warmer and the amount of incoming solar radiation is greater. The results of
the present study are in good agreement with those of seasonal variation of mixing height in Delhi
(Padmanabhamurty and Tangirala, 1990).
Due to the highest mixing height in April among all the seasons, good vertical mixing of
contaminants may take place in this month especially during the afternoon. In July, pollutants will be removed
by wet deposition (i.e., Rainout and Washout) and their concentration will be relatively lower though the mixing
heights are low. January and October may be regarded as the worst months for diffusion or vertical mixing of
contaminants.
Ventilation Coefficient
Ventilation coefficient is an important parameter for assessing high pollution potential. It is a parameter that
indicates the capacity or efficiency of the atmosphere in dispersing air pollutants released from local sources.
Low ventilation coefficients indicate poor dispersion capacity of the atmosphere for air pollutants.
It is the product of mixing height and average wind speed within the mixing layer. Winds used in these
calculations are the averages over the entire mixing layer. The average wind speed through the mixing layer was
calculated as a simple average of the wind speed aloft (up to mixing height) as determined by radio sonde data of
wind speed and surface wind speed. Monthly mean ventilation coefficients for five years have been calculated
for 00, 03, 06, 09, 12, 15, 18 and 21 GMT for all the representative months at Bhopal and Gwalior and are
presented in Tables 4 and 5.
Based on the analysis of observations reported above, it can be concluded that April has the highest
ventilation coefficient (in the afternoon) and July has the lowest ventilation coefficient. The mean afternoon
ventilation coefficient is nearly the same in July and October. Higher values of ventilation coefficient are mainly
due to the very high mixing heights during daytime while low values of ventilation coefficients during nighttime
are due to the lower values of mixing height and light prevailing winds. Highest mean maximum values of

7. ventilation coefficients are found mostly at 09 and 12 GMT whereas mean minimum are observed at 00 and 03
GMT.
Table 4: Diurnal Variation of Mean Ventilation Coefficients (m2
s-1
) at Bhopal
SEASONTIME 00 03 06 09 12 15 18 21
Winter 365 621 2862 5471 5112 1251 736 673
Pre monsoon 1057 3281 5521 14555 13046 8972 2999 1499
Monsoon 1050 1935 4669 4751 4786 4234 2125 1568
Post monsoon 445 935 2428 4892 4570 2192 1190 664
Table 5: Diurnal Variation of Mean Ventilation Coefficients (m2
s-1
) at Gwalior
SEASONTIME 00 03 06 09 12 15 18 21
Winter 324 589 2782 5491 5056 1345 786 590
Pre monsoon 1100 3331 5589 12988 14034 9037 3067 1278
Monsoon 998 1887 4632 4823 4826 4279 2056 1634
Post monsoon 412 975 2408 4902 4598 2216 1088 478
Pollution Potential
Gross (1970) criteria for assessing/forecasting pollution potential is widely used by US National Meteorological
Center and Atmospheric Environment Service, Canada. Gross (1970) criteria for assessing high pollution
potential is that the morning mixing depths should be 500 meters and transport wind speed  4 meter/sec and
afternoon ventilation coefficient should be  6000 m2
/Sec and the transport wind speed should be  4 meter/sec.
Due to the non-availability of any standard criteria for assessing high pollution potential in India, an attempt has
been made in the present study to delineate periods of high pollution potential at Bhopal and Gwalior
applying/adopting the above criteria.
As per above criteria, mean monthly morning (minimum) and afternoon (maximum) mixing heights,
average transport wind speed through the mixing layer and morning (minimum) and afternoon (maximum)
ventilation coefficients for the four representative months viz., January (Winter), April (Pre-monsoon), July
(Monsoon) and October (Post monsoon) at Bhopal and Gwalior have been plotted in Fig. 3 (a-c).
Applying Gross (1970) criteria of forecasting high pollution potential, it may be seen that in the present
study morning periods have high pollution potential in all the seasons. This pollution potential decreases
gradually during the day and eventually disappears in the afternoon at both the stations. It was also observed that
afternoon periods have low pollution potential in the month of April and July at Bhopal and in the month of
April, July and October at Gwalior. Better dispersion of pollutants is expected in the summer (April) season due
to higher mixing heights and ventilation coefficients, and poor in winter (January) followed by post-monsoon
(October) season due to lower mixing heights and ventilation coefficients.
The afternoons of April are expected to be better periods for vertical mixing of contaminants. The pollutants will
be removed through wet deposition in the month of July and their concentration will be lower even though
mixing height and ventilation coefficient are low. The results show that the pollutants will be well dispersed in
the months of April and July. The months of January and October might be regarded as the worst months for
dispersal/diffusion of contaminants at both Bhopal and Gwalior.

8. Bhopal
0
500
1000
1500
2000
2500
Jan Apr Jul Oct
Mixingheight(m)
Min
Max
Gwalior
0
200
400
600
800
1000
1200
1400
Jan Apr Jul Oct
Mixingheight(m)
Min
Max
Fig. 3 (a) Seasonal mean mixing height
Bhopal
0
2
4
6
8
Jan Apr Jul Oct
Meanwindspeed(m/s)
Max.
Min.
Gwalior
0
1
2
3
4
5
6
Jan Apr Jul Oct
Meanwindspeed(m/s)
Min
Max
Fig. 3 (b) Seasonal mean wind speed throughout the mixing layer
Bhopal
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
Jan Apr Jul Oct
Ventilationcoefficient(m2/s-1)
Min
Max
Gwalior
0
2000
4000
6000
8000
10000
12000
Jan Apr Jul Oct
Ventilationcoefficient
Min
Max
Fig. 3 (c) Seasonal mean ventilation coefficients

9. Conclusion
Low winds were observed in January and high in April for both the stations. The predominant winds were N and
NE. The dilution of pollutants is expected in April and accumulation in January. From wind direction, it can be
concluded that no major polluting industry should be set up in the S and SW sector of the capital region of
Madhya Pradesh (Bhopal). Among the four representative months, good dispersal of pollutants takes place in
April and July where as poor dispersal/ diffusion takes place in January and October and during the nighttime of
all the months. Of all four months Bhopal shows highest frequencies of inversion layers in January and lowest in
July. Hence January may be the worst month for mixing of pollutants whereas July is better.
During the four months the highest afternoon mixing height and ventilation coefficient occurred in
April. Morning hours had a high pollution potential which decreases gradually with the time of day. Thus, it can
be concluded from this study that pre-monsoon (April) and monsoon (July) months have a high carrying capacity
of pollutants. Winter (January) and post monsoon (October) months have less dispersal capacity. Night and early
morning hours have less dispersal capacity of pollutants due to stable atmosphere accompanied by light/weak or
no winds.
Acknowledgement
ACP acknowledge with thanks for the meteorological data of Bhopal and Gwalior provided by the Indian
meteorological department.
References
1. Gross, E., 1970. The national air pollution potential forecast program. ESSA Tech. Memo. WBTM
NMC 47, U.S. Department of Commerce.
2. Holzworth, C. G. 1974. Climatological aspects of the composition and pollution of the atmosphere.
W.M.O., Tech. Note No. 139, W.M.O., Geneva.
3. Hosler, C. R. 1961. Low-level inversion frequency in the composition and pollution of atmosphere.
Mon. Wealth. Rev. 89: 319-339.
4. Kallos, G., P. Kassomenos and R. Pielke 1993. Synoptic and mesoscale circulations associated with air
pollution episodes in Athens, Greece Boundary Layer Met. 63: 163-184.
5. Katsoulis, B.D. 1988. Aspects of occurrences of persistent surface inversions over Athens basin, Greece.
Theo. App. Climatology 39: 98-107.
6. Millan, M.M, R. Salvador, B. Acena, J. C. Bezares, M. Martin, M. Pujadas, J. Goberna, A. Albizuri and
M. Navazo 1988. Field measurement of plume dispersion in a complex coastal site. Castellon. In proc.
COST 611: Workshop on field measurements and their interpretation, Villefranche Sur Mer, France-4,
May 1988.
7. Munn, R. E. 1970. Air pollution meteorology in manual on Urban Air Quality Management. Regional
Publications, European Series No. 1, WMO, Copenhagen.
8. Munn, R.. E. 1970. Air flow in urban areas, Urban climates. W.M.O. Tech. Note No. 108, 15-39,
W.M.O., Geneva, Switzerland.
9. Munn, R.. E., and M. S. Hirt 1976. Recent Canadian trends in air pollution meteorology. Naturaliste
Can. 96: 711-724.
10. Ogawa, Y., P. G. Diosey, K. Uehara and H. Ueda 1985. Wind tunnel observation of flow and diffusion
under stable stratification. Atmospheric Environment 19: 65-74.
11. Padmanabhamurty, B. and R. S. Tangirala 1988. An assessment of the assimilative capacity of the
atmosphere at Delhi. International conference on tropical micrometeorology and air pollution., New
Delhi.
12. Padmanabhamurty, B. and R. S. Tangirala 1990. An assessment of the assimilative capacity of the
atmosphere at Delhi. Atmospheric Environment 24 (A): 845-848.

10. 13. Rai, B. and B. Padmanabhamurty 1993. Dispersion climatology of Patna and Gaya, Mausam 44: 199-
204.
14. Sadhuram, Y. and K. P. R. Vittalmurty 1986. Diurnal and seasonal variation of pasquill stability class at
coastal station. Mausam 37: 187-192.
15. Turner, D. B. 1964. A diffusion model of an urban area. J. Appl. Meteorology 3: 83-91.
16. Wark, K. and C. F. Warner 1976. Air pollution, its origin and control. IEP A Dun Donnellyey
Publishers, New York.
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