Preface   Modern industrial society produces a large number of gases and particulate matter in sufficient quantities to harm human, animal and plant life. The amount of pollutants released in the atmosphere by fixed or mobile anthropogenic sources, is associated with economic activity. The progressive increase in urbanization in recent years, although has positive role in developmental process, but at the same time it imposes unending challenges, such as inadequate water supply, improper sanitation, and waste disposal, traffic congestion, environmental pollution and in general unsafe social environment. Deterioration of air quality is a major environmental problem in many urban centers in both developed and developing countries. Root cause of urban air pollution is the continuous rise in vehicle population. Other causes are exponential growth of population, rapid proliferation of industries and technological development. Encroachments on roadside, mixed vehicles on roads, lack of smooth traffic flow, congested and narrow roads resulting in traffic jams are the main causes of air pollution. Urban air pollution is characterized by high concentration of suspended particulate matter, oxides of sulphur and nitrogen resulting primarily from increased use of vehicles. Trees are immovable and are continuously exposed to pollutants in air and soil. They play an important role in maintaining ecological balance by actively participating in the cycling of nutrients, gases and air pollutants. Some trees are sensitive to pollution and act as bio-indicators of air pollution; hence it is more effective to see the impact of pollution on vegetation especially on roadside trees. Many trees are effective for trapping and absorbing air pollutants and act as sink to several air pollutants, hence trees play an important role in the improvement of urban air quality. Pollutants adversely affect plants with respect to their metabolic activities, which depend on the concentration of pollutants in the atmosphere, type of plant species, physiological stage and the season too. Plants improve air quality and thereby seem to be the suitable marker of air pollution and can be used to draw or edit air quality maps.

Ever since industrial revolution altered the whole gamut of economic activity at least two hundred years ago, the path of economic growth including its modified form economic development had appeared unending and limitless. The whole focus of economic activity is to produce mere goods and services for use by the mankind so that life could be more comfortable and satisfying. Increasing population and increased needs of more goods and service was also seen as a hindrance or limitation in the march towards economic growth and development.

AIR Air is a non-homogenous mixture of gases, solid particles, and liquids; It consists of gases and particles with small settling velocity that exhibit stability in a gravitational field. Atmosphere has four major layers Troposphere from 0-17km., Stratosphere from 17-50km., Mesosphere from 50-90 km. and Ionosphere is from 90-100 km. (95% of the air by weight is contained in the Troposphere i.e. from 0-17 km).

AIR POLLUTION FROM AUTO EXHAUST Motor vehicles are the major source of a number of pollutants, in particular carbon monoxide (CO),nitrogen oxides (NOx), unburnt hydrocarbons (HC),ozone (O3) and other photo chemical oxidants and lead (Pb) and, in smaller proportions Total Suspended Particulate Matter (TSPM), sulphur dioxide (SO2) and volatile organic compounds.

Particulate Matter Anthropogenic emissions of particulate matter include fossil fuel (diesel and petrol) combustion from mobile and stationary sources (Rogge et. al., 1993a-c), biomass burning (Forest fires, landfills, agricultural activities and incinerators) (Oros and Simoneit, 1999) natural gas (Rogee et. al., 1993c), wood (McDonald et. al., 2000) and coal combustion (Mastral and Callen, 2000).

Effect of Air Pollutants on Plants   Elements of those air pollutants which accumulate in plants (S from SO2, heavy metals from anthropogenic emissions etc.) may be used for specific bio-indication of possible effects caused by these pollutants, and for mapping their spatial and temporal distribution. Measuring accumulated components in plants rather than directly in the environment, provides the dual advantages of an integrated rather than a momentary value, and of a biological content rather than a mere concentration (Stocker and Gluch, 1990).

The response of plants to air pollution can be understood by analyzing the physiological and biochemical parameters of plants. Physiological Parameters The epidermal cells are the first to interact with the air pollutants and also lack chloroplast. Epidermal cells hence cannot remove excess sulphur through the production and release of H2S. Damage to plants by air pollutants depends upon the amount of pollutants entering the cells and their reactivity with cellular constituents. Plants regulate the entry of gaseous molecules through stomatal movement thereby affecting the photosynthesis and transpiration. Response of plants to gaseous pollutants varies from species to species. This is due to differences in the stomatal conductance, aperture size and permeability of plasma membrane (Yunus et al., 1996).

Atmosphere serves as the medium through which pollutants are transported and dispersed. While being transported, the pollutants undergo chemical reactions, which may be lethal or scavenged by chemical or physical process/method. But it all exclusively depends upon the meteorological conditions (Lee et .al, 1994). Historic air pollution episodes reveal that atmospheric conditions influence the pollutant concentrations as well as their toxicity (Goldsmith & Friberg, 1976; Wichmann et.al, 1989 and Pope et.al, 1992). However, the location, duration of release, height as well as the pollutant concentrations are also important, which effect the secondary pollutant transformation under the influence of meteorological conditions, but the atmospheric behavior is independent of their sources (Holzworth, 1974).

Metals Metals are ubiquitous in the modern industrialized environment. Heavy metals like cadmium, iron, molybdenum, lead, nickel, tin and zinc are present in the environment in trace concentrations. These metals are universally present in soil, water, air and biota (Freedman, 1995). Global anthropogenic heavy metal inputs to ecosystem through air, water and soil have increased substantially world wide over last century (Nriagu, 1996).

Through the sharing of experience of developed countries, which faced the massive health problem due to vehicular pollution in the past and remedial measures adopted by them, it is needed to avoid mistakes made in the past and instead introduce effective measures for the future to reduce or confine the damage that has already been incurred. A progressive policy of motor vehicle emission control strategy, which may be more feasible/affordable, has to be adopted for solving immediate air pollution problems. Uncontrolled growth of vehicular fleet and its emission is taking place in the urban areas, which must be controlled/regulated in order to prevent future disaster. Because of economic development and speed of motorization expected over next decades this problem will become more vulnerable and even greater, If control measure are not adopted timely. It is suggested that planning must begin to provide alternatives to the motor vehicles and to reduce emission of the vehicles. The country without high capital resources will face challenging problems for evolving control strategy that will be acceptable both economically and socially.

Urban Air Pollution and Its Impact on Roadside Plants Urban Air Pollution Modern industrial society produces a large number of gases and particles in quantities to harm human, plant or animal life. The amount of pollutants released to the atmosphere by fixed or mobile anthropogenic sources is generally associated with the levels of economic activity. Deterioration of air quality is a major environmental problem in many urban centers in both developed and developing countries. Automobiles constitute a major source of air pollution in the urban areas. Motor vehicle emissions result from fuel combustion or evaporation. The most common types of transport fuel are gasoline and diesel. CO2 and water vapors are the main products of the combustion, emitted in vehicle exhaust. The major pollutants emitted from the vehicles are particulate matter (suspended fine and ultra fine), sulphur dioxide, oxides of nitrogen, carbon monoxide and metals.

Plants play an important role in maintaining ecological balance by actively participating in the cycling of nutrients and gases like carbon dioxide, oxygen and air pollutants. Sensitivity and responses of plants to air pollutants is variable. Some plants are sensitive and act as bio indicators of air pollution (Kozhouharov et. al. 1985, Guderian, 1998). Others which are tolerant may act as sink to air pollutants. However this aspect needs more investigation for their use as indicators of air pollutants and in abatement of air pollution.

Air Estimation of Total Suspended Particulate Matter (TSPM) and Respirable Suspended Particulate Matter (RSPM) Requirements Instrument High Volume Sampler (HVS) APM 415-411 (Envirotech Instrument India), Respirable Dust Sampler (RDS) APM 451 (Envirotech Instrument India) with midget impinger containing absorbing solution were used.

Pollution is continuously increasing in India. To control ambient air pollution CPCB has prescribed National Ambient Air Quality Standards

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