Bangkok Metropolitan Region - Thailand (BMR), one of the major metropolitan areas in the world, is a bustling upper-middle class megacity composed of Bangkok city proper and five surrounding provinces. With an actual population of approximately 15 million, it is the central hub for commerce and tourism in the Southeast Asian (SEA) region. In the past decades, Bangkok has experienced extraordinary economic development and urban expansion, all the while displaying notable concern regarding the ambient air pollution and its adverse effects on human health. In this study, 16-years of air quality monitoring data were collected from 25 stations in BMR, which are operated by the Thailand’s Pollution Control Department. Data for O3, PM10, NOx, CO and SO2 were analyzed temporally with a particular focus on long-term, seasonal and diurnal variations. The data were also analyzed spatially to identify the hotspots and flow of air pollution in the region. These investigations were performed to assess the evolution of air quality in BMR over the past 16 years and identify areas of potential concern. Analysis of the data indicated that PM10, NOx , CO and SO2 were in a moderate decline over the 16 years, while O3 concentration has risen steadily throughout this time period. The results and findings of these investigations are discussed with a perspective to provide policy recommendations for air quality improvements in BMR.