Our understanding of the global aerosol change is rather limited, although it is well known that aerosol forcing could affect the global radiative budget, hydrological processes, carbon, nitrogen and sulfur cycles, as well as climate change. To understand the wide range effects of aerosols, it is key to obtain aerosol characteristics at high spatio-temporal resolutions. In this study, we try to map the global variations of the aerosol optical depth (AOD) using two aerosol products retrieved from MODIS (Moderate Resolution Imaging Spectroradiometer) satellite instrument. It is found that the global average AOD is 0.126 over the last decade (2003–2012). The highest and the lowest AOD occurred in 2007 and 2010, respectively. AOD variations between land and ocean, north and south hemispheres, among seven continents and four oceans were also explored. It is interesting to find that high concentrations of aerosols are mainly distributed in regions where developing countries are located (Asia and Africa), and an increasing trend could also be observed. Seasonal variations of AOD (air quality) can also be noted, which is decreasing in the north hemisphere from spring, summer to autumn and winter, but increasing in the south hemisphere.