Analysis of variation trends and causes of aerosol optical depth in Shaanxi Province using MODIS data

The temporal and spatial variations and causes of aerosol optical depth (AOD) in Shaanxi Province were investigated based on the Moderate Resolution Imaging Spectroradiometer (MODIS) derived aerosol data for the period of March 2000–February 2012. The results showed that the distribution of aerosol was largely affected by topography and local economic activities. Heavy aerosol loading and increasing tendency in AOD was observed in Guanzhong, Hanzhong and Ankang basin, while a reverse tendency was revealed in most other regions. The spatial distribution of aerosol Angstrom wavelength exponent was predominantly related to vegetation coverage in Shaanxi. Airborne dust from ground is an important source of coarse mode aerosols. Vegetation improvement indicated by an increase in normalized difference vegetation index (NDVI) and a reduction in dust weather led to a gradual decrease in coarse mode AOD to the north of Qinling Mountains in Shaanxi, while anthropogenic activities led to an increase in fine mode AOD in other areas except those covered by forests. The main aerosol type gradually shifted to the urban industrial type in Shaanxi.