1-km Aerosol Optical Depth From MODIS Measurements Over Hong Kong

diometer (MODIS) aerosol retrieval algorithm was developed to derive aerosol properties at a global scale, suitable for climate studies. Under favorable conditions (clear sky and over dark surfaces), the standard 10 10 km MODIS aerosol products are also useful on regional scales to monitor aerosol distributions and transports. However, the 10-km resolution is insufficient to depict aerosol variation on local or urban scales, due to inherent aerosol variability as well as complex surface terrain. In this study, we have modified the MODIS algorithm to retrieve aerosol optical depth (AOD) at 1-km resolution over Hong Kong, a city of just over 1000 km2 with very complex surface features. Accompanied by the increased spatial resolution are new aerosol models derived with single-scattering albedo (SSA) around 0.91–0.94 to accom-modate higher aerosol absorption encountered in Hong Kong than that was presumed for MODIS standard products (SSA 0 97) over the region. The derived AOD data are compared to handheld Microtops II sunphotometer observations at the Hong Kong Uni-versity of Science and Technology and other locations across Hong Kong. Retrieval errors within 15 % to 20 % of sunphotometer measurements are found. Moreover, when compared with the standard 10-km AOD products, the 1-km AOD data are much better correlated with PM 10 measurements across Hong Kong, suggesting that the new 1-km AOD data can be used to better characterize the particulate matter distribution for cities like Hong Kong than the MODIS standard products. Index Terms—Aerosols, air pollution, remote sensing. I