Fine particles (PM_2.5) have adverse impacts and risks on air quality and human health. The present research focuses on the concentrations of PM_2.5, air quality index (AQI), and assessment of hospital admissions due to COPD attributed to PM_2.5 particle levels in Tehran during the last 10 years from 2011 to 2020. The effects of meteorological parameters (i.e., wind speed, humidity, and temperature) and AQI on PM_2.5 concentrations were examined using data from 21 active monitoring stations of the Air Quality Control Company (AQCC) and Mehrabad Meteorological Station. The health impact assessment of PM_2.5 in terms of hospital admissions due to chronic obstructive pulmonary disease (COPD) was obtained by the AirQ_2.2.3 model. Based on the results, the annual average PM_2.5 concentrations decreased from 2011 through 2020. The results also show a significant effect of meteorological data on the changes in PM_2.5 particle concentration. We also noticed that reduction of annual PM_2.5 concentration from 38.55 (AQI = 104.08) in 2011 to 28.59 μg m⁻³ (AQI = 83.87) in 2020 could prevent 779 (by about 70%) premature deaths, and the estimated number of excess cases human respiratory system attributed to PM_2.5 at central relative risk (RR) during the last decade was 6158 persons. Also, air quality got from unhealthy for sensitive groups of people to moderate air quality. Finally, any reduction in concentrations of PM_2.5 in Tehran can reduce the number of hospital admissions due to COPD significantly. The results of investigations on PM_2.5 particles have shown the need for the national clean air program policies and the necessity of urgent actions to improve the air quality to human health in Tehran.