Longitudinal Study of Air Pollutants in Indian Metropolises: Seasonal Patterns and Urban Variability

This study investigates the longitudinal trends and spatial variability of atmospheric trace gases and particulate matter (PM_2.5) in five major Indian metropolitan areas: Delhi, Chennai, Hyderabad, Kolkata, and Mumbai, over the period from 2016 to 2020. Utilizing data from satellite remote sensing and ground-based monitoring stations, we analyze the seasonal and daily variations in concentrations of key pollutants, including nitrogen dioxide (NO₂), sulfur dioxide (SO₂), ozone (O₃), and PM_2.5. The study reveals distinct seasonal patterns influenced by meteorological conditions, urban activities, and regulatory measures. Elevated levels of pollutants are observed during winter months, particularly in Delhi, attributed to temperature inversions and biomass burning. Comparative analysis highlights significant urban variability, with Delhi exhibiting the highest pollution levels, while Chennai shows the lowest. Statistical analysis reveals that Delhi records the highest average daily concentrations of CH₄ (1869.50 ± 31.08 ppbv) and PM_2.5 (106.99 ± 83.49 µg/m³), while Chennai consistently records the lowest levels of CH₄ (1836.82 ± 26.78 ppbv) and PM_2.5 (33.42 ± 27.85 µg/m³). These findings provide critical insights into the temporal dynamics and spatial heterogeneity of air pollution, essential for devising targeted air quality management strategies in Indian cities.