Estimating PM₁ concentrations from MODIS over Yangtze River Delta of China during 2014–2017

Compared to the space-borne estimation of PM_2.5 (particulate matter with aerodynamic diameter ≤2.5 μm), the investigation of PM₁ (≤1 μm) remains less intensive and thus unclear. Here we estimated four years (2014–2017) of ground-level PM₁ concentrations from MODIS aerosol optical depth (AOD) in attempt to gain a better understanding of much finer particles. The Yangtze River Delta (YRD) region, with a relatively dense ground-based PM₁ station network, was selected as the study area. The geographically and temporally weighted regression (GTWR) model simultaneously accounting for spatial and temporal variability existing within various predictors was constructed. Validation of satellite-estimated PM₁ against ground-measured PM₁ yields a high consistence, significant improvement over previous work (R² = 0.74 VS 0.59, RMSE = 13.02 μg/m³ VS 22.5 μg/m³). This suggests the PM₁ estimates from GTWR model are reliable and robust enough to obtain large-scale fine particle contents. The population exposure of air pollution in the YRD region, therefore, has been analyzed by calculating population-weighted mean PM₁ concentrations, which reaches as high as 37.22 μg/m³. Further analysis indicates that near half the people live in locations with high-level PM₁ concentration (>35 μg/m³), which has profounding implication for improving our understanding of human exposure to fine aerosol particles.