A Green Bioindicator Approach to Air Quality Monitoring through Plants

Air pollution poses significant threats to urban vegetation by inducing physiological and biochemical stress, thereby affecting plant growth and survival. This study evaluates the impact of air pollution on four commonly occurring tree species — Ficus religiosa, Mangifera indica, Polyalthia longifolia, and Ricinus communis — across four sites with varying pollution levels: an industrial zone, a roadside urban area, a suburban campus, and a rural control site. Key biochemical and physiological parameters, including ascorbic acid content, total chlorophyll content, leaf extract pH, and relative water content, were measured and integrated into the Air Pollution Tolerance Index (APTI) to assess species tolerance. Results indicated that plants from industrial and roadside urban sites exhibited reduced ascorbic acid and chlorophyll levels, lower leaf extract pH, and diminished relative water content, reflecting pollution-induced oxidative and physiological stress. Among the species studied, Polyalthia longifolia and Ficus religiosa demonstrated higher APTI values and greater resilience to pollution stress, while Mangifera indica showed higher sensitivity. These findings highlight the potential of Polyalthia longifolia and Ficus religiosa for urban afforestation and green belt development aimed at mitigating air pollution and improving urban environmental quality.