Due to rapid urbanization, Delhi experiences frequent pollution events, and the particulate matter load exceeds the prescribed limit often. This study analyzes nanoparticles (10 to 1090 nm) during different emission scenarios, seasonal and meteorological conditions in two phases: April to June 2021 (Period I) and October to November 2021 (Period II). Period I experienced around 31% less concentration of particles (similar to 2.4 x 10(4) cm(-3)) due to lockdown restrictions and, on the other hand, particle concentration increased by 35% compared to normal conditions due to the sudden rise in firework emissions in Period II. Except for the post-Diwali phase (10(4) cm(-3) to 10(5) cm(-3)), the concentrations lie between 10(3) cm(-3) and 10(5) cm(-3). The Aitken modes contribute 10 to 30% of total concentration in both periods. Particles in nucleation and accumulation modes contribute 30 to 40%, 20 to 30%, 15 to 25%, and 35 to 50% in Periods I and II, respectively. Number concentration-based studies are essential for estimating the potential impacts on human health due to air pollution. The study provides information regarding vehicle emission-based particle concentration under various emission scenarios in urban cities, which is crucial for estimation of emissions, health impact assessment, future policy formulation and strategy measures.