Satellite-Based Analysis of Black Carbon Pollutant in Tehran, Iran: Ground Validation and Future Outlook

Black Carbon (BC) is a critical air pollutant with significant impacts on public health and climate. This study provides a comprehensive analysis of two-decade BC concentration trends over Tehran, Iran, by integrating satellite observations with ground-based measurements. We utilized monthly mean BC surface mass concentration data from the MERRA-2 reanalysis product from 2002 to 2021 and compared it against daily measurements from a ground-based Aethalometer station (2014–2017). The results reveal a significant discrepancy between the two datasets, with MERRA-2 underestimating ground-level BC concentrations by approximately a factor of four. A Wilcoxon signed-rank test confirmed that the datasets are statistically distinct (p < 0.001). Despite the difference in magnitude, MERRA-2 successfully captures the strong seasonal cycle of BC, with pronounced peaks in winter and minimums in summer, driven by meteorological conditions. A Seasonal Autoregressive Integrated Moving Average (SARIMA) model was developed based on the 20-year historical MERRA-2 data to forecast future trends. The model demonstrated strong predictive performance and projects a continuation of the current elevated concentrations and seasonal patterns. This study highlights the utility of satellite data for long-term trend analysis while underscoring the necessity of ground-based data for accurate local air quality assessment and public health applications. The forecast provides a quantitative baseline for future environmental planning in Tehran.