Background: This study examined temporal variations in six air pollutants (PM₂.₅, PM₁₀, SO₂, NO₂, O₃, CO) in Ahvaz, Bandar Abbas, and Bushehr during 2018–2022, focusing on pre- and during-COVID-19 periods.
Methods: SO₂, NO₂, CO, and O₃ data were obtained from the TROPOMI sensor onboard Sentinel-5P (7 × 7 km resolution) via Google Earth Engine (GEE). PM₂.₅ and PM₁₀ concentrations were estimated from Aerosol Optical Depth (AOD) data from MODIS MCD19A2 (1 km) using a regression model calibrated with ground monitoring data. Records with >30% cloud cover or missing values were excluded, and monthly and annual means were calculated. Satellite observations were bias-corrected via linear regression against ground-based data and downscaled using bilinear interpolation. Inter-city comparisons used independent t-tests; pre- vs. during-pandemic differences were assessed using paired t-tests.
Results: Ahvaz recorded the highest mean PM₂.₅, PM₁₀, SO₂, and CO levels. In most cases, pollutant concentrations were higher before COVID-19, particularly PM₂.₅ and PM₁₀ in Ahvaz and Bushehr (p < 0.05). Correlations between satellite and ground-based PM₂.₅ and PM₁₀ were strong and significant in Ahvaz and Bushehr, but weak or insignificant for SO₂, NO₂, and O₃.
Conclusion: Integrating satellite and ground-based measurements enables accurate, cost-effective air quality monitoring. Reductions in certain pollutants, especially particulate matter, were associated with decreased industrial activity and transportation during the pandemic. However, spatial variability and local meteorological conditions substantially influenced pollution patterns.