Quantifying links between aerosol optical depth and rapid urbanisation induced land use changes, Hangzhou, China, 2000–2020

The decline in air quality is thought to be due to rapid land use/land cover (LULC) changes near metropolitan areas that are undergoing rapid urbanisation. Here, we quantify the characteristics and relationship between the aerosol optical depth (AOD) index and LULC changes in Hangzhou, China, since the 21st century using multispectral satellite remote sensing data. The regional study results show that the correlation between the operational AOD observations (MOD04_3K) at 3 km resolution and the in situ AOD measurements available in Hangzhou ranges from 0.48 to 0.80, and their root mean square error (RMSE) < 0.30. During the past two decades, Hangzhou has been in the stage of rapid urbanisation, and the area of construction land has increased significantly, mainly converted from cultivated land and forests. The correlation coefficients between the AOD and the changes of cultivated land, forest land, grassland and construction land in Hangzhou were 0.36, 0.86, 0.61 and 0.63, respectively, indicating a strong correlation except for the cultivated land. Finally, the temporal evolution of the correlation coefficients between the cultivated land and building land are positively correlated with AOD, while from the trend of the correlation curve, grassland, woodland and AOD show negative correlations.