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Journal Article 
The effects of air pollution on stomatal clogging, carbohydrate and chlorophyll contents in certain roadside plants 
Ahmad, Z; Qadir, SA 
Pakistan Journal of Botany
ISSN: 0556-3321
EISSN: 2070-3368 
Karachi is the most industrialized and largest city in Pakistan where increased economic activity is continuously spoiling the environment. The city centre is particularly suffering from air pollution due to heavy traffic, large number of vehicles pollute the air by adding exhaust gases. Carbon, rubber, smog reactants, hydrocarbons and oxides of nitrogen are released into the environment as a consequence of incomplete combustion in the automobile engines.
Prindle & Charles (1962) studied the effects of motor vehicles upon animals and plants. They described that automotive emissions consisting principally of carbon monoxide, carbon dioxide, the oxides of nitrogen, and a variety of unburned or partially oxidized hydrocarbons, participate in the formation of photochemical smog. These smog substances appeared to be more dangerous than the original emission. They found that automotive emission damaged the agricultural crops. Darley et al (1963) studied the effects of pollution derived from automobiles on plant damage. Different gases and compounds found in the exhaust were damaging to the leaves of a variety of crop plants, and the physical and chemical systems within the plants were disrupted by the photoxicants. Sitnikova (1963) made a physiological study of photosynthesis and the dynamics of carbohydrate and chlorophyll accumulation in trees and shrubs under different growth conditions (an ore concentration plant, a botanical garden and a metallurgical plant). He found that considerable amount of gas and dust in the vicinity of industrial plants caused an increase in photosynthetic rate in trees most resistant to smoke and gas like Russian olive, elm, ash, maple balsam and poplar. In view of these considerations, the effect of air pollution on stomatal clogging, carbohydrate and chlorophyll content of certain road-side plants was studied.