According to UNEP’s Global Environment Outlook (GEO) 6 for Cities, air pollution is currently the largest environmental health risk in cities. As such, cities are an integral part of the solution in fighting air pollution and the climate crisis. Cities in low and middle-income countries need evidence-based solutions to improve air quality. This publication documents the story of air quality over 15 years (2005-2020) in Seoul, Incheon, and Gyeonggi, Republic of Korea. It presents a comprehensive analysis of various air pollutants (PM2.5, NOx, SOx, ozone, and greenhouse gases like Methane, along with their sources and health impacts and documents the progress made during the period. It highlights the initiatives undertaken by the government of Korea, such as the Clean Air Conservation Act and the National Fine Dust Reduction Plan to improve air quality. Exploring the linkages between air pollution and climate change, the report recommends future actions to further reduce air pollution in Korea. By providing insights and recommendations on improving air quality and protecting public health, the report aims to serve as a valuable reference for policymakers, researchers, and citizens in Republic of Korea and beyond.