This study investigates the variation in particulate matter (PM_2.5 and PM₁₀) concentrations in Gazipur, Bangladesh during three distinct phases: before, during, and after the COVID-19 pandemic by utilizing secondary data from the Continuous Air Monitoring Stations situated in Gazipur. Gazipur is one of the major urban cities and a hub for the garments industry in Bangladesh. Since the establishment of Gazipur City Corporation in 2013, a number of large-scale construction and development projects have been initiated there which eventually deteriorated the air quality. The findings indicated consistently high pollution levels before the COVID-19 pandemic, especially during winter months. Seasonal factors, like low temperatures and stagnant air, lead to increased PM levels, although monsoon rains temporarily improved air quality. During the COVID-19 lockdown in 2020, PM_2.5 and PM₁₀ levels decreased by 6.5% and 53.7% respectively, based on annual average compared to 2019 because of reduced industrial and transportation activities. Nevertheless, levels immediately returned to pre-pandemic figures following the lifting of major restrictions. Even during the lockdown, PM concentrations were above Bangladesh's National Ambient Air Quality Standards and World Health Organization’s Air Quality Guidelines as evidenced by the annual average value of 235 µg/m³ for PM₁₀ in 2021. The peak PM_2.5 and PM₁₀ levels post COVID-19 were recorded as 307.1 and 339 µg/m³ respectively. These findings emphasize the necessity of adopting long-term measures to improve air quality. Measures must encompass more stringent emissions regulations, additional CAMS establishment, sustainable urban development, and improved public awareness to safeguard public health and ensure clean air in Gazipur.