A new way of using MODIS data to study air pollution over Hong Kong and the Pearl River Delta

Aerosols are the main air pollutant in Asia. In this paper, the MODIS level 2 aerosol optical depth (AOD) products derived by NASA were validated with in situ sun-photometer observations over Hong Kong (HK). The MODIS AOD values were correlated with mass concentrations of respirable suspended particulates (RSP) measured at air quality monitoring stations over HK and Macau. Correlation between RSP and AOD were found to be statistically significant, suggesting that the satellite data is very useful for aerosol-related air pollution studies. Compared with concentrations measured from ground-based air quality monitoring networks, the AOD data cover a much larger area and have much better spatial resolution. Combining with meteorological information, the AOD data also proved to be very useful for the understanding of RSP variations at air quality monitoring stations. An example of using AOD data to help understand a pollution event over the PRD will be presented. Finally, monthly-mean distributions of AOD over Eastern China showed a distinct local maximum over the PRD, separated from high AOD areas to the north, suggesting that the aerosol problem over the PRD are mostly regional. Remote-sensing from space has provided a new and powerful way to study air pollution. To fully utilize this technique for air quality studies, the combination of a lidar and an X-band satellite receiver (for the MODIS data) is recommended. The AOD fields are vertically integrated products, together with the vertical profiles of extinction coefficients provided by a lidar, the surface distribution of aerosol could be derived.