INTRODUCTION
The quality of air affects the quality of life and human respiration and the quality of air can change as the weather changes from day to day and even hour to hour. Our environment comprises of a very large and intertwining complex of water, air, soil and biological life which includes nature and all living beings; the environment is affected by human activities and vice versa (Tabatabae, et al., 2012).
The quality of air has an impact on the quality of life of humans. Air pollution is a result of industrialization and urbanization and it is a major problem of cities (Hamraz et al., 2014).
Natural factors such as windstorms, extreme temperature and dust, add particles and gases to the air, also human activities, industrial and agricultural plants and vehicles are factors that result in the presence of such materials in the air. Across the Middle East, people have always contended with excessive heat, dust storms, shortage of rainfall and harsh environment: thus air pollution has more effect on people’s lives in this region (United Nations Environment Program, 2002).
Among the damages caused by air pollutants, the most significant ones occur in the leaves of plants. These damages include chlorosis and necrosis of leaves. Infact, plants exposed to pollutants show a wide variety of responses (Deepalakshmi, et al., 2013).
Air pollution has become an important factor in environmental degradation by increasing the concentration of gases and introducing the suspended particulate matter to the atmosphere. The developing countries have experienced a progressive degradation in air quality due to rapid development in industrial and urban sectors in the last three decades (Lindgren and Saravanakumar, 2009).
Air pollution has both direct and indirect impacts on animal and plant physiology by disturbing normal respiratory mechanisms and changing the morphological and biochemical characteristics (Govindaraju, et al., 2010).
Plants have a very close interrelationship with the environment and any altered condition of the atmosphere has a strong impact on its physiology and biochemistry. The damage to the vegetation as a result of air pollution is important from the stand point of both agricultural production and ecological balance (Sharma and Rama, 2008).
Air pollution tolerance index (APTI) is an inherent quality of plants to encounter air pollution stress which is presently of prime concern particularly of urban areas of the world. Since plants are stationary and continuously exposed, chemical pollutants from the surrounding atmosphere cause injury. Air pollution injury is proportional to the intensity of the pollution (Rao, 2006).
Air pollution tolerance index based on the following parameters such as ascorbic acid content, chlorophyll content, leaf extract pH and relative water content had been used for identifying tolerance levels of plant species (Singh and Rao, 1998).
According to Mashita and Pise (2000), there is a scale of APTI value which indicates the APTI value between 30-100 – the species is tolerant; APTI values between 17-29 – the species is intermittently tolerant and plants registering APTI value in the range of 1-16 are considered as sensitive; APTI value lower than 1 is branded as highly sensitive.
Air pollution tolerance index is used by landscapers to select plant species tolerant to air pollution (Yan-ju and Ding, 2008).
Air pollution tolerance index has been used to rank species in their order of tolerance to air pollution (Raza and Marlhy, 1988).
This study aims to determine the Air pollution tolerance index values of selected plant species commonly found in the vicinity of road sides with respect to the above biochemical parameters. Plant response towards the pollutants from the surrounding atmosphere can be used to assess the quality of air that provides an easy warning signal for the trend of air pollution in the area.
The objectives of this study are as follows: