Effect of vegetation on urban climate and healthy urban colonies

Effect of vegetation on urban climate and healthy urban colonies

Energy and Buildings, I5 487 - 16 (1990/91) 487 - 491 Effect of Vegetation on Urban Climate and Healthy Urban Colonies S. H. 0. BHAGYA RAZA, ...

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Energy and Buildings,



- 16 (1990/91) 487 - 491

Effect of Vegetation

on Urban Climate and Healthy Urban Colonies

S. H.




Ecology and Environmental

Biology Laboratory,

LAKSHMI Department


The role of plants in developing a healthy atmosphere is very desirable in the context of deteriorating environment resulting from increased urbanization, industrialization and improper environmental management. This investigation has attempted to screen plants for their ability to improve the design and development of healthy environments around buildings and urban centres of Hyderabad. Ability index values were computed on the basis of canopy area, physiological characters of trees growing in polluted environments, pollution stress and population load. Azadirachta indica, Pithecolobium dulce and Cassia fistula are suggested for plantations around buildings and urban centres for minimizing pollution, Certain susceptible trees like Pongamia glabra and Polyalthia longifolia have been suggested in the diagnosis and investigation of air quality through biological means.


The development of healthy urban colonies is becoming an increasing problem in the context of rapid industrialization and population explosion. The growth of industries introduces dangerous problems of toxic emissions of gases and particulate matter. Such air pollutants have high dispersion rates and could even effect human habitations located several miles away [l]. While controlling the sources of pollutants by engineering methods is a long-term practice, the management of existing pollutants in the air to minimize their effects on urban colonies has recently gained a lot of attention. One of the safest ways of minimizing pollutant effects on urban colonies is by landscaping the colonies with pollutionresistant trees [2,3]. The present investigation is focused on unfolding the ability of different 0378.7788/91/$3.50

and G. SHYLAJA of Botany, Osmania

University, Hyderabad

500 007 (India)

trees to purify the environment based on different morphological and physiological characters against the total pollution load of a given area, and to suggest suitable trees and designs for plantations around buildings.



Hyderabad, one of the biggest industrialized cities in India, contains various types of industries, namely, smelters, pharmaceutical, distilleries, refineries, quarries, etc. All these industries are located in the Nacharam, southeast of Hyderabad, and it is recognized as the worst polluted area. In addition, there are also big urban colonies located in and around industrial areas. Hence Nacharam was selected for the investigation. Leaf samples from 11 trees growing in Nacharam under isoecological conditions were collected and analysed for chlorophyll [4], ascorbic acid [ 51, nitrogen [6] relative water content [ 51, sulfate [7] and area of canopy. The analysis of gaseous air pollutants was done for SO,, NO,, SPM and dustfall [ 81. A collection of leaf samples was done with a cane under isoecological conditions of temperature, water, soil and sunlight. Leaf samples were collected at a height of 12 feet. Six leaf samples were collected from each type of tree and mean values were presented. Dust deposition on leaf surfaces was calculated by washing the leaves thoroughly with 100 ml of distilled water in a polythene bag. The water from the polythene bags was poured into a preweighed crucible and kept for evapor:t’ion. After evaporation the difference in weight of crucible is taken as weight of dust deposition per unit area of leaf surface. The growth and survival of trees under polluted atmospheres depends much on possessing different pollution-resistant characteristics and the degree of pollution load. In view BJ> Elsevier Sequoia/Printed

in The Netherlands


of this, the above-mentioned parameters of a tree are considered as pollution-resistant factors and the different pollutants like SO,, NO,, SPM, settleable dust and population (human and cattle) as pollution load. The ratio of these two factors is determined by the following newly suggested formula. Ability

Index of a tree =

Area of


i canopy Pollution (


Internal physiological resistance x Population


x 100


where the canopy area = xr2, r = radius of the ground cover, internal physiological resistance = A(T+N) +R

R = relative water content (%) Pollution stress = SO, t NO, + SPM + settleable dust Population (human + animal) = 500/km”. The area of canopy and internal physiological resistance are responsible for the ability of the vegetation to grow and survive, hence the sum of these parameters is taken in the numerator. As this ability is inversely related to the product of pollution stress and population, the product of pollution stress and population is placed in the denominator. The ratio is multiplied by 100 to obtain an empirical figure in terms of percentage. The index thus obtained for the deciduous trees is multiplied by two as these plants produce a new crop of leaves every year.

where A = ascorbic acid (mg/lOO g dry wt.) T = total chlorophyll (wdg dry wt.) N = nitrogen (%) TABLE



Canopy area of trees Name of tree

Area of canopy (ft*)

Albizzia lebbeck Annona squamosa Azadirachta indica Caesalpinia pulcherima Cassia fistula Eugenia jambolana Phoenix sylvestris Pithecolobium dulce Pongamia glabra Polyalthia longifolia

12.56 14.44 21.98 18.84 12.56 12.09 6.28 9.42 15.70 1.53


The canopy area of trees is presented in Table 1. The maximum area of 21.98 ft2 was observed in Azadirachta indica and minimum of 1.53 ft’ was observed in Polyalthia longifolia. The moderate values of 6.28 - 18.84 were observed in Albizzia, Pongamia, Caesalpinia, etc. Physiological resistance values comprising total chlorophyll, ascorbic acid, nitrogen and relative water content are presented in Table 2. Maximum values of chlorophyll and ascorbic acid were observed in Azadirachta indica. Caesalpinia, Cassia and Dalbergia were found to have a high nitrogen content. High internal physiological resistance values of 283.51 and 279.53 were observed in Azadirachta indica and Dalbergia sissoo respectively.


Internal physiological Name of the tree

Albizzia lebbeck Annona squamosa Azadirachta indica Caesalpinia pulcherima Cassia fistula Dalbergia sissoo Eugenia jambolana Phoenix sylvestris Pithecolobium dulce Pongamia glabra Polyalthia longifolia


of trees

Total chlorophyll


(mgig dry wt.)

(mg/g dry wt.)




Relative water content (%)

Internal resistance

11.6 11.2 11.7 11.2 11.0 11.2 7.0 10.8 8.8 10.6 10.2

7.4 15.8 16.3 8.2 14.7 14.7 5.8 6.0 15.1 8.9 6.7

1.1 1.5 1.6 2.2 2.3 2.7 1.8 2.1 2.1 1.7 1.6

73.0 67.5 76.5 73.7 74.2 75.2 76.2 78.8 86.0 85.7 80.5

166.98 268.16 283.51 183.58 269.71 279.53 127.24 156.20 250.59 195.17 159.56




Details of air pollutants Name of the pollutant



12.0 6.0 194.0 23.2

NO, SPM Dust fall (metric

tons/km2 per m)

* In the formula, values are converted TABLE

to mg/m3.


Dust deposition

on different trees

Name of the tree

Dust deposition

Albizzia lebbeck Annona squamosa Azadirachta indica Caesalpinia pulcherima Cassia fistula Dalbergia sissoo Eugenia jambolana Phoenix sylvestris Pithecolobium dulce Pongamia glabra Polyalthia longifolia

34.6 33.4 37.5 48.3 48.0 41.6 34.1 23.7 76.3 25.6 22.9

TABLE Ability



Index value of trees Ability

Azadirachta indica Dalbergia sissoo Cassia fistula Annona squamosa Pithacolobium dulce Pongamia glabra Caesalpinia pulcherima Albizzia lebbeck Polyalthia longifolia Phoenix sylvestris Eugenia jambolane

2.6 2.5 2.4 2.4 2.2 1.8 1.7 1.5 1.4 1.4 1.2


Foliar sulfate (%) in some trees


Name of the tree

fistula can remove maximum dust from the atmosphere, whereas Pongamia glabra and Polyalthia longifolia showed minimum dusttrapping efficiency. The Ability Index values for trees have been calculated on the basis of a newly proposed formula (Table 5). Trees like Azadirachta indica, Cassia fistula, Dalbergia sissoo, Annona squamosa and Pithecolobium dulce have the high values ranging from 2.2 - 2.6, while Eugenia jambolana and Albizzia lebbeck values are low, ranging from 1.2 - 1.5. The foliar sulfate levels in different trees are presented in Table 6. Pongamia glabra and Polyalthia longifolia were found with a high content of sulfate while a minimum value of 0.03 was found in Annona squamosa.

Index value

The annual averages and four-hour peak levels of different pollutants, namely SO,, NO,, SPM and dustfall, are presented in Table 3. Though annual average values were less, the four-hour peak concentrations were found to be very high. Suspended particulate matter was found to be very high with annual means of 194 p g/m3. The dust-trapping efficiency of trees was analysed and was found to vary among trees (Table 4). It was observed that Cuesalpinia pulcherina, Pithecolobium dulce, and Cassia

Name of the plant


Albizzia lebbeck Annona squamosa Azadirachta indica Caesalpinia pulcherima Cassia fistula Dalbergia sissoo Eugenia jambolana Phoenix sylvestris Pithecolobium dulce Pongamia glabra Polyalthia longifolia

0.093 0.03 0.06 0.054 0.086 0.097 0.058 0.046 0.12 0.11 0.115


In recent times, the establishment of new industries and factories was immediately followed by the mushrooming of housing colonies in the areas surrounding the industries. While this type of encroachment on industrial surroundings on one hand minimizes the time period of workers attending the factory, on the other hand it maximizes the pollution effect on the surrounding vegetation, buildings and human beings. Aerial emmissions from factories cause a wide variety of health effects [9, lo]. However certain trees generally possess potential to decrease the pollution by acting as a labyrinth. Hence the knowledge of trees and their capacity to cleanse the air environment would go a long way in establishing healthy surroundings


around industries and colonfes. For this purpose in the present investigation, Ability Index values are calculated by the ratio between plant resistance factors and total stress comprising aerial emissions and population in a given area. Trees like Azadirachta indica, Eugenia jambolana, Cassia fistula and Pithecolobium duke, having a bushy type of canopy and broad leaves, are able to trap much of the dust and act as sinks for pollutants. Plants with conical architecture, with narrow leaves with a smooth texture like Polyalthia longifolia and Phoenix syluestris, have a minimum value in trapping dust (Figs. 1 and 2). Trees with simple leaves are most suitable for dust trapping as they can expose a uniform area, for the settling of dust. Though the dissected and compoundleaved trees lack a well-defined surface, their total leaf surface area will generally be more than simple-leaved trees. Similar observations were made by Singh and Rao [ll]. The gases and fumes which are mainly generated indoors, will decrease in concentration with an increase in the airflow rate. Plants are also responsible for the air or wind flow to some extent and for dispersing the pollutants. Azadirachta indica, Cassia fistula and Pithecolobium duke, having a bushy type of canopy with more leaves all over, are responsible for rapid and more air filtration and act as purifi-






Fig. 1. Different shapes of canopies ing colonies.

suitable for landscap-

ers of air than those plants with conical and congested leaves (Fig. 2). It was also opined by Gilbert [9] that the efficiency of plants in absorbing pollutants is such that they can produce pockets of relatively clean air. Bernatsky [2] suggested that green belts might help to reduce air pollution. Plant response to a pollutant also depends on its internal resistance, mainly due to chlorophyll, ascorbic acid, nitrogen and relative water content. The chlorophyll concentration was minimum in Polyalthia and Pongamia. Similar observations were made by Bhatnagar et al. [12] and Chaphekar [ 131. Azadirachta indica and Cassia fistula had more internal resistance due to high ascorbic acid, chlorophyll and relative water contents. On the basis of Ability Index values, trees have been classified into sensitive and tolerant species and are arranged in descending order of their Ability Index values. Higher index values show more resistance and the reverse of it susceptibility. In shows Azadirachta indica, Cassia fistula, Dalbergia sissoo and Pithecolobium dulce the Ability Index is high. Tolerant trees are also called ‘accumulator indicators’ where they absorb pollutants in higher quantities and can accumulate them without experiencing any damage or sometimes derive a fertilizer effect from sulfur and nitrogen pollutants such as SO, and NO,. As such, the tolerant trees observed in the present investigation showed high values of sulfate accumulation and the sum of physiological factors reflected less damage. Therefore these plants are designated as pollution sinks for reducing the pollutant level in the environment. Plants like Polyalthia longifolia and Pongamia glabra having a low index value act as susceptible trees and can be used for identifying and monitoring of air pollutants. Similar observations were made by Singh and Rao




Fig. 2. Different ping.




shapes of leaves suitable


for dust trap-

It should be mentioned that plant species known to be tolerant or sensitive in one region may not be the same in another region, as the physiological factors may change from place to place depending on adaptational and climatic factors. So the Ability Index values thus determined help in screening and selecting appropriate plants for growing urban colonies in a given area only. The Ability Index values of trees obtained by this method


folia and Pongamia glabra are suggested monitoring of the air environment.



The authors thank the Head of the Department of Botany, Osmania University, for providing laboratory facilities and encouragement. Fig. 3. Plantation industry.



an urban colony


compared well with their observed tolerance level under field conditions. A model showing the method of plantation of trees around industrial and residential zones is also developed (Fig. 3). Mixed plantations are more preferable to avoid the epidemic attacks of selective pests and absorption of nutrients from soils. Mixed plantations with different-shaped canopies would help the air to disperse at a faster rate. The plantation should be made in the form of successive circles around the colonies to minimize the influx of pollutants. However around industries the design should make an easy path for the efflux of emmissions and should maximize the emmissions interaction with vegetation.


The proposed formula is found useful in determining the ability of trees in cleaning air and in assessing air quality. Azadirachta indica and Cassia fistula, etc., are suggested for controlling pollution, while Polyalthia longi-

REFERENCES 1 0. B. Mudd and T. T. Kozlowski, Responses of Plants to Air Pollution, Academic Press, New York, 1975, pp. 102 - 114. 2 A. Bernatsky, PFOC. First European Congress on the Influence of Air Pollution on Plants and Animals, Centre for Agricultural Publishing and Documentation, Wageningen, The Netherlands, 1968, pp. 383 - 95. 3 N. Faller, Effect of atmospheric SO, on plants, Sulfur Institute J., 6 (1970) 57. 4 G. I. Arnon, Copper enzymes in isolated chloroplasts polyphenol oxidase in Bata vulgaris, Plant Physiol., 24 (1949) 1 -15. 5 A. Singh, Practical Plant Physiology, Kalyani Publishers, New Delhi, 1977, p. 266. 6 C. S. Piper, Soil and Plant Analysis, Inter-Science Publishers Inc., New York, 1966. I G. B. Patterson, Sulfur, in D. F. Boltz (ed.), Colorimetric Determination of Non-Metals, Inter-Science Publishers Inc., New York, 1958, pp. 216 - 308. 8 Selected Methods of Measuring Air Pollutants, Publication No. 24, WHO, Geneva, 1976, 112 p. indicators of air pollution, 9 0. L. Gilbert, Biological Ph.D. Thesis, University of Newcastle, 1968. 10 K. Jales and J. M. Dave, Techniques for particulate sampling and analysis, An evaluation, Indian J. Air Pollut. Control, 2 (1979) 29 - 32. S. K. Singh and B. N. Rao, Evaluation of plants for their tolerance to air pollution, Proc. Symposium on Air Pollution Control, Indian Institute of Technology, Delhi, 1983, pp. 218 - 224. A. R. Bhatnager, A. B. Vora and T. S. Patel, Measurement of dust fall on leaves in Ahmedabad and its effect on chlorophyl, Indian J. Air Pollut. Control., 6 (1985) 17 - 91. S. B. Chaphekar, Effects of atmospheric pollutants on plants in Bombay, J. Biol. Science., 15 (1972) 1 - 16.