Urban Air Quality Assessment: Variability and Behavior of Fine Particles under Tehran’s Climatic Conditions

Due to rapid industrialization, population growth, and urban development, Tehran faces serious air pollution challenges. In this study, the concentration of fine particles with an average diameter of 0.4 µm was monitored at four stations across Tehran over a one year period. The results indicated that the annual mean concentration ranged from 0.33 µg/m ³ in winter to 0.70 µg/m ³ in summer, exhibiting a clear seasonal pattern. Concentrations increased during warm months due to higher temperatures, lower relative humidity, atmospheric stability, and urban activities, while they decreased in cold months under the influence of precipitation and atmospheric cleansing. Statistical analysis revealed a relatively strong inverse relationship between relative humidity and particle concentration (R ²  = 0.73) and a direct correlation between temperature and particle concentration (R ²  = 0.81). Spatially, stations near urban pollution sources recorded higher concentrations, whereas peripheral stations showed lower levels. SEM analysis indicated a diverse particle composition of dual origin (natural and anthropogenic), with finer particles primarily from combustion and mobile sources, and coarser particles from dust, construction, and mineral sources. These findings highlight the critical role of climatic conditions and local sources in fine particle variability and underscore their importance in urban air quality management and forecasting.