Evaluating Roadside Vegetation as a Pollution Buffer Along Major Transport Routes: A Case Study from Delhi.

High urbanization and industrialization have resulted in a significant increase in air pollution impacting artificial and natural ecosystems. Roadside vegetation often act as a line of defence against air pollution to mitigate the impacts of pollutants. This demands a scientific investigation to assess the role of roadside plantation for better management and planning for urban sprawl where selected trees could be grown to mitigate the impacts of harmful pollutants. Thus, the present study investigates how variations in roadside vegetation density influence pollutant behaviour by comparing two traffic-intensive urban corridors in Delhi: Site 1 – Mundka which is a low-vegetation roadside environment, and Site 2 - Vishwavidyalaya (North Campus) which is characterised by continuous mature tree cover. Long-term ambient datasets (Jan 2024–Nov 2025), short-term real-time monitoring, and i-Tree Eco assessments of sampled roadside trees were integrated to quantify pollutant dynamics and vegetation-mediated mitigation.

Across the 23-month dataset, PM₁₀ concentrations at Site 1- Mundka (mean: 267.7 µg/m³) were consistently higher than at Site 2 - North Campus (186.1 µg/m³), representing ~1.4-fold greater particulate burden despite similar diurnal traffic signatures and strong regional coupling (r = 0.898). Distinct pollutant regimes emerged: Site 2 - North Campus showed elevated combustion pollutants (NO, NOx, CO), whereas Site 1 - Mundka exhibited higher NO₂, O₃, and coarse-particle dominance (PM₂.₅/PM₁₀ = 0.36). Field observations further revealed substantial dust accumulation on Mundka’s tree leaves, likely suppressing stomatal activity and reducing pollutant-removal efficiency.

i-Tree Eco modelling demonstrated a striking multi-fold difference in ecosystem services: trees at Site 2 - North Campus removed up to four times more pollutants than those at Site 1 - Mundka, with peak monthly removal reaching 34 kg compared to 4–5 kg. Higher leaf-area availability, mature DBH classes, and greater species diversity at North Campus also supported substantially greater carbon storage, sequestration, and oxygen production.

Overall, the findings highlight that well-maintained, continuous roadside tree corridors can meaningfully moderate pollution peaks along major transport routes. As several countries increasingly adopt planned roadside greening, the results underscore the potential of structured vegetation strategies to strengthen air-quality resilience at both urban and national scales in India.