Air Pollution Tolerance Index of climber plant species to develop Vertical Greenery Systems in a polluted tropical city

Urban greenery can provide a cost-effective and eco-friendly technique to help reduce air pollution in compact urban areas. Urbanization generally replaces natural vegetation with concrete structures. Greenery can be reintroduced into such urban areas by development of vertical greenery systems (VGSs) on building walls. Such plants must be selected based on their air pollution tolerance level. Air pollution tolerance index (APTI) is one such index which is based on four properties of plant leaves such as ascorbic acid content, leaf extract pH, relative water content and total chlorophyll content. In this study in Varanasi, India, air pollution was monitored at seven sites to know the air quality status, based on which two sites were selected for evaluating APTI. Twenty eight climber plant species commonly found near a polluted site (site-1) were selected and their APTI was evaluated. APTI of same set of plants were also analyzed at relatively less polluted rural site (site-7) for comparative study. Linear regression analysis has revealed a high positive correlation between APTI a d ascorbic acid content (R2 = 0.8676) and positive correlation between APTI and Chlorophyll content (R2 = 0.4957). On the basis of higher APTI values (greater than 17), eleven climber species i.e. Ipomoea palmata, Antigonon leptopus, Thunbergia grandiflora, Clerodendrum splendens, Aristolochia elegans, Quisqualis indica, Vernonia elaeagnifolia, Petrea volubilis, Adenocalymma comosum, Cryptolepis buchanani and Jacquemontia violacea have been identified at polluted urban site to develop vertical greenery systems in this compact tropical city.