A Comparative Review of Air Quality in India’s Most Populated Capitals: Analyzing AQI Based on Environmental pollutants PM2.5, Carbon Monoxide (CO), Nitrogen dioxide (NO2), Sulfur dioxide (SO2), and Ozone (O3)

Air pollution in India has become a significant environmental and public health issue, particularly in densely populated urban centers. This paper reviews and compares the Air Quality Index (AQI) in five of India's most populous and polluted capital cities—New Delhi, Mumbai, Kolkata, Chennai, and Bengaluru—focusing on key pollutants: Particulate Matter (PM2.5 and PM10), Carbon Monoxide (CO), and Sulfur Dioxide (SO₂). Data for this review were sourced from the Central Pollution Control Board (CPCB), WHO reports, and city-level environmental monitoring agencies. (1) Each city's AQI trends are analyzed to highlight the major contributors to air pollution, such as vehicular emissions, industrial activities, and seasonal factors like stubble burning and weather patterns. New Delhi consistently ranks as the most polluted city with hazardous PM2.5 and PM10 levels, while other cities like Mumbai and Chennai, though polluted, exhibit lower AQI levels due to geographical and climatic conditions. This review also examines the health risks posed by prolonged exposure to these pollutants and evaluates current mitigation efforts by the government. The study emphasizes the need for more stringent policies, sustainable urban planning, and public awareness campaigns to reduce air pollution in these urban areas. Further research is recommended to assess the long-term impact of current policy measures and explore alternative solutions for improving urban air quality.