Tolerance and performance assessment of common subtropical vegetation growing along a highway for bio-monitoring and abatement of air pollution

Roadside vegetation is inevitably exposed to airborne pollutants and demonstrates a wide range of tolerance and sensitivity towards it. In the present study twenty indigenous plant species were screened for Air Pollution Tolerance Index (APTI) and Anticipated Performance Index (API) by accessing their biochemical and socio-economic attributes for the development of green belts along highways as a cost-effective and eco-friendly strategy for air pollution abatement. Simultaneously, ‘Criteria’ air pollutants; CO, SO₂, NO₂, O₃, Pb and Particulate matter were also analysed to assess biomonitoring potential of the species screened for APTI and API. Concentration of PM₁₀ and PM_2.5 in the ambient air were found beyond the National Ambient Air Quality Standards (NAAQS, PM₁₀: 100 µg/m³ and PM_2.5: 10 µg/m³) and ranged between 36.43 and 288.6 and 24.32–184.23 µg/m³, respectively, whereas, SO₂, NO_x, O₃, Pb and CO were within the permissible limits (PL: 80, 80, 180, 1 µg/m³ and 04 mg/m³ respectively ranged between 8.41 and 19.37, 9.31–28.28, 0.06–41.95 and 0.01.0–0.106 µg/m³, and 0.19–1.77 mg/m³, respectively. The APTI and API values served as composite index of ecological health revealed that Ficus religiosa, Alstonia scholaris, Cassia fistula, Azadirachta indica, and Neolamarckia cadamba for which APTI values were found to be ≥ 17 indicating tolerance against adverse air quality and can be utilized in the development of green barrier along the highways, whereas, Tecoma stans, Nerium oleander, Psidium guajava, Nyctanthes arbor-tristis, Ricinus communis, and Hibiscus rosa-sinensis, displayed APTI values of less than 11, suggesting their potential use in biomonitoring of air pollution. Further, evaluation of Dust Capturing Potential (DCP) of different plant species revealed that species like Platanus occidentalis, Mangifera indica, and Psidium guajava are highly effective in capturing dust. This insight is crucial for urban areas where dust pollution is a significant concern. This dual approach which integrates APTI and API ensures that the selected plants are not only biologically capable of withstanding ambient pollution but also socio-economic viability for large-scale planting. The study identifies specific plant species that exhibit high tolerance to air pollution. These findings are therefore valuable for urban planners and environmentalists in quest to mitigate air pollution through natural based solution not only as physical barrier to pollutants but also ensures increased green cover in urban area.