Air quality in the world’s largest cities has become one of the most important environmental and public-health challenges of the 21st century. Rapid urbanization, increasing vehicle ownership, industrial activity, construction, energy consumption, and population growth have contributed to high levels of PM2.5, PM10, nitrogen dioxide (NO₂), ozone (O₃), sulfur dioxide (SO₂), and other air pollutants. AQI and Major Air Pollutants Pollutant Main Sources Major Concern PM2.5 Vehicles, combustion, industry, biomass burning Penetrates deep into lungs PM10 Construction, road dust, industry Respiratory irritation NO₂ Vehicles, power plants, combustion Respiratory problems O₃ Photochemical reactions Lung irritation SO₂ Coal and industrial combustion Respiratory health CO Incomplete combustion, vehicles Reduces oxygen transport PM2.5 is…