<p>Air pollution is a persistent environmental challenge in rapidly urbanizing megacities such as Delhi, India. While many tree species can mitigate pollution through biochemical and structural adaptations, current screening approaches, such as the Air Pollution Tolerance Index (APTI), provide only partial insights when applied in isolation. This study evaluated seasonal variation (monsoon and winter) in biochemical markers, leaf morphological traits, and pollution tolerance of ten native urban tree species. APTI was calculated using standard biochemical parameters, and principal component analysis was applied to integrate biochemical and structural responses under contrasting pollution regimes. Results revealed pronounced seasonal plasticity, with clear trade-offs between optimising photosynthesis and structural reinforcement. Specific traits, notably leaf dry matter content (LDMC) and specific leaf area (SLA), exhibited inverse seasonal dynamics, reflecting shifts in resource allocation strategies. Although APTI correlated strongly with structural traits, species with high APTI but weak morphological adjustment were less reliable under prolonged or fluctuating stress. These findings highlight the limitations of using APTI alone and demonstrate the need for a trait-based framework that combines tolerance indices with adaptive morphological responses. The proposed integrative approach offers a scalable tool for urban forestry planning, facilitating evidence-based selection of resilient tree species for sustainable pollution mitigation and ecosystem service delivery across diverse climatic contexts.</p>