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Pollution-Gobbling Trees And their Significance In Urban Air Quality

Air pollution may be defined according to the origin of the phenomena that help determine it: one which are natural causes (natural fumes, decomposition, volcanic ash) or second anthropogenic causes which are the result of human activities (industrial and civil emissions).

Air pollution is a global challenge that annually causes millions of premature fatalities. It is restricted not only to the developing countries but also to the developed nations, with towns struggling in specific to maintain the values of air quality to the suggested ones and protect human health. Total exposure to air pollution is often disproportionately affected by the relatively short amount of time spent commuting or in the proximity of traffic.

Air pollutants in urban and industrial areas may be absorbed, accumulated or integrated into the plant body and the toxicity may injure them to some degree. The level of injury will be high in sensitive species and low in the tolerant ones. Sensitive species are useful as early warning indicators of pollution and the tolerant ones help in reducing the overall pollution load leaving the air relatively free of pollutants.

Some plants are not only sensitive to pollutants but they show specific responses which makes them useful as biological indicators. Tolerant plant species represent the greatest possibility for reducing the injury caused by air pollutants. Since the degree of resistance strongly depends on the type of pollutant. The exact knowledge of those types and their concentrations are necessary for the successful utilization of this method of pollution abatement. Systematic monitoring of the soil and climate of polluted areas, as well as air pollution levels, should be carried out for early detection of any negative trends. From the results of such studies along with a consideration of specific species tolerance, and possible risks of plant injury from air pollutants, a system can be developed which will provide a clean and healthy environment.

A method of classifying plant species as sensitive, intermediate and tolerant may not be entirely satisfactory since different stages in the life cycle of a plant are likely to differ in their sensitivity or resistance to pollution. Nevertheless, such a classification provides a basis for the determination and selection of certain tolerant plant species capable of reducing the impact of air pollution.

APTI (Air pollution tolerance index) is a unique index because it incorporates four different biochemical parameters: total chlorophyll, pH of leaf extract, ascorbic acid and relative water content.

APTI =

where,

A = ascorbic acid content in mg/g of dry weight,

T = total chlorophyll in mg/g of fresh weight,

P = pH of leaf extract,

R = relative water content (%)

On the basis of APTI and some relevant biological and socio-economic characteristics, the anticipated performance of plant species in a GB (green belt) plantation was calculated. Plant categories were graded as best, excellent, good, moderate, and poor. Species belonging to the first four categories were recommended.

Planting of Ficus benghalensis (Banyan), Ficus religiosa (Peepal), Ficus mysorensis (Mysore Fig tree) and Albizia lebbeck (Siris tree) in town squares and on the outskirts of villages and towns may considerably reduce air pollution. Planting of trees bearing stony fruits in areas of fluoride pollution or seed fruits in areas of SO2 pollution is not recommended.

Mangifera indica (Mango) was the most tolerant plant to grow in industrial areas and can be expected to perform well. It has a dense plant canopy of evergreen like foliage, which may afford protection from pollution stress. The economic and aesthetic value of this tree is well known and it may be recommended for extensive planting as a first curtain.

Ficus benghalensis (Banyan), Ficus infectoria (Pilkhan) and Mimusops elengi (Spanish cherry) were judged to be excellent performers, while Artocarpus integrifolius (Jackfruit), Dalbergia sissoo (Indian rosewood), Eugenia jambolan (Malabar plum) and Saraca indica (Ashoka) qualified for the very good performer category.

Besides these 10 good performing species, 12 were found to be unsuitable as a pollution sink because of their lower anticipated performance but have been planted in industrial areas for their aesthetic value and other economic uses. The latter species are attractive plants that certainly enhance the aesthetic value of the industrial/urban areas.

Thus, an evaluation of anticipated plant performance might be very useful in the selection of appropriate species. From the viewpoint of air pollution mitigation plants judged best find their use in GB plantation. The planting recommendation above is not for any specific industry.

In addition to API (Anticipated performance index), the selection of tree species for GB development will be based on the regional extent of the pollution load together with soil quality, rainfall, temperature and human interactions. The development of adequate GB information regarding climate, pedosphere and human interactions is crucial. In any GB development, monoculture is not advisable due to its climatic factor and other environmental constraints.

GB with multiple species is preferred for maintaining species diversity, rational utilization of nutrients and for the long term health of the trees. Well planned GB will develop a favorable micro-climate to support different microorganisms that will steadily improve soil quality, depending upon topo-climatological conditions and regional ecological status.

The effectiveness of the GB depends on the selection of the right type of plant species-particular tolerant of pollutants to that area. An ideal plant for use in a GB should have the following characteristics:

  1. The fast growth rate for quick development of a canopy
  2. Strong branches for a durable canopy to withstand storms
  3. Large leaf size for enhanced retention of pollutants
  4. Dense foliage for better trapping of pollutants
  5. Relatively good tolerance to  insects and diseases
  6. Tolerance to soil compaction and nutrient stress
  7. The long life span for, extended longevity of the GB itself

To conclude with the article we can say that rather than a shallow and simplified way to deal with plant trees in settings to battle contamination impacts, one needs to have a comprehension of the types of trees that will have the ideal contamination alleviation impact with extra-biological system administrations. Indeed, even in compensatory afforestation, you have to give due thought to a plant’s affectability record (known as Air Pollution Tolerance Index) and carbon sequestration nature to diminish contamination heap of the separate site before planting any sapling.

References:

G. Krishnaveni, K. Kiran Kumar, Air pollution tolerance index of selected

plants in Vijayawada city, Andhra Pradesh

National Air Quality Index, Central Pollution Control Board (Ministry of Environment, Forests & Climate Change) Government of India

World Health Organizations Global Ambient Air Pollution

http://maps.who.int/airpollution/

Research Done by:

Sourabh Vishwas Raskar, Data Scientist, Quantela

Sumedh Rajan Ghatage, Data Scientist, Quantela

In association with: Sanjiv Kumar Jha, Chief Data Scientist, Quantela

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