Satellite observations of the aerosol direct radiative effect during a pollution episode in Nanjing, China, using high-resolution HJ-1 CCD imagery

摘要

The charge-coupled device imageries from the Chinese environmental satellites (HJ-1) with 30 m spatial resolution are used in this study to investigate the shortwave aerosol direct radiative effect (ADRE) during a pollution episode in March 2013 over Nanjing City. The Deep Blue algorithm is used to retrieve the aerosol optical depth (AOD) and the results are then validated using ground-based data. The mean values of the AOD in Nanjing at 550 nm are 0.41, 0.54, and 0.79 on 3, 4, and 7 March 2013, respectively, with fitting degree 0.796. The spatial aerosol distribution indicates that the pollution is induced by local emission, accumulated as a result of suitable weather conditions, and then spread by the wind. The ADRE results at the surface and at the top of the atmosphere (TOA) are then calculated using radiative transfer model. The mean values and standard deviations of the ADRE on 3, 4, and 7 March are -75.6 +/- 21.3, -98.8 +/- 16.6, and -138.1 +/- 26.0 W m(-2) at the surface and -3.7 +/- 3.8, -5.2 +/- 4.6, and -8.1 +/- 5.9 W m(-2) at the TOA, respectively. The results show that although aerosols can cause warming at the TOA over a highly reflectivity surface, the total radiative effect corresponds to the cooling of both the Earth-atmosphere system and the surface at the expense of heating the atmosphere.